While the majority of the Promoted Products we sell to our advertisers are placed on Twitter, we also generate advertising revenue by placing advertising products that we sell to advertisers on third-party publishers’ websites, applications or other offerings.
Data Licensing and Other We generate data licensing and other revenue by (i) offering “Gnip”-branded products and data licenses that allow our data partners to access, search and analyze historical and real-time data on our platform, which data consists of public Tweets and their content, and (ii) providing mobile advertising exchange services through our MoPub exchange.
Our data partners generally purchase licenses to access all or a portion of our data for a fixed period.
We recognize data licensing revenue as the licensed data is made available to our data partners.
In addition, we operate a mobile ad exchange and receive service fees from transactions completed on the exchange.
Our mobile ad exchange enables buyers and sellers to purchase and sell advertising inventory and matches buyers and sellers.
We have determined we are not the principal in the purchase and sale of advertising inventory in transactions between third party buyers and sellers on the exchange.
Therefore we report revenue related to our ad exchange services on a net basis.
## Table 0 ##
2015 Compared to 2014.
Revenue in 2015 increased by $815.0 million compared to 2014.
On a constant currency basis, revenue in 2015, using the prior year’s monthly exchange rates for our settlement currencies other than the U. S.  dollar, would have increased by $896.7 million or 64% compared to 2014.
In 2015, advertising revenue increased by 59% compared to 2014.
On a constant currency basis, advertising revenue in 2015, using the prior year’s monthly exchange rates for our settlement currencies other than the U. S.  dollar, would have increased 65% compared to 2014.
The substantial majority of our advertising revenue was generated from our owned and operated platform.
Advertising revenue generated from the sale of our advertising services on our owned and operated platform in 2015 was $1.80 billion as compared to $1.24 billion in 2014.
Advertising revenue generated from the sale of our advertising services on third party publishers’ websites, applications and other offerings in 2015 was $194.2 million as compared to $11.4 million in 2014, which increase was driven, in part, by the acquisition of TellApart.
The overall increase in advertising revenue was primarily attributable to a 107% increase in the number of ad engagements offset by a 23% decrease in average cost per ad engagement in 2015 compared to 2014.
The increase in ad engagements was primarily the result of our move to auto-play video in late 2015, as well as growth in our advertising revenue generated from third party publishers’ websites, applications and other offerings, and an increase in ad load.
The decrease in average cost per ad engagement was due primarily to the shift to auto-play video, which delivers more engagement at a much lower average cost per engagement than click-to-play video ads.
Advertising revenue continued to be driven by growth in demand for our advertising products, particularly video and website card formats as well as growth in our advertising base.
In 2015, data licensing and other revenue increased by 52% compared to 2014.
The increase was primarily attributable to growth in mobile advertising exchange services as well as the increase in data licensing fees from the offering of “Gnip”-branded products for a full year in 2015 as compared to the partial year in 2014.2014 Compared to 2013.
Revenue in 2014 increased by $738.1 million compared to 2013.
In 2014, advertising revenue increased by 111% compared to 2013.
The increase was primarily attributable to a 175% increase in the number of ad engagements in 2014 offset by a 23% decrease in average cost per ad engagement in 2014 compared to 2013.
Advertising revenue also benefited from sales of our Promoted Products on our mobile applications as well as from an increase in international revenue.
In 2014, data licensing and other revenue increased by 109% compared to 2013.
The majority of this increase was attributable to a full year of revenue generated from mobile advertising exchange services in 2014 as compared to the partial year of revenue generated in the prior year.
Cost of Revenue Cost of revenue includes infrastructure costs, other direct costs, amortization of acquired intangible assets and capitalized labor costs, allocated facilities costs, as well as traffic acquisition costs (“TAC”).
Infrastructure costs which consist primarily of data center costs related to our co-located facilities, which include lease and hosting costs, related support and maintenance costs and energy and bandwidth costs, as well as depreciation of our servers and networking equipment, and personnel-related costs, including salaries, benefits and stock-based compensation, for our operations teams.
TAC consists of costs we incur with third parties in connection with the sale to advertisers of our advertising products that we place on third-party publishers’ websites, applications or other offerings collectively resulting from acquisitions, and from our organically-built advertising network, Twitter Audience Platform.
Many of the elements of our cost of revenue are relatively fixed, and cannot be reduced in the near term to offset any decline in our revenue.
## Table 1 ##
2015 Compared to 2014.
In 2015, cost of revenue, which included TAC of $121.8 million, increased by $282.9 million compared to 2014.
The increase was primarily attributable to a $113.7 million increase in TAC, a $79.5 million increase in networking, hosting and data center costs related to our co-located facilities, a $76.3 million increase in depreciation expense related to additional server and networking equipment and amortization of acquired intangible assets, and a $24.1 million increase in other direct costs, offset by a $10.7 million decrease in personnel-related costs, mainly driven by a decrease in average employee headcount and stock-based compensation expense.2014 Compared to 2013.
In 2014, cost of revenue increased by $179.6 million compared to 2013.
The increase was primarily attributable to a $75.5 million increase in depreciation expense related to additional server and networking equipment and amortization of acquired intangible assets, a $60.2 million increase in networking, hosting and data center costs related to our co-located facilities, a $27.0 million increase in allocated facilities and other supporting overhead costs due to the continued expansion of our real estate footprint and increase in support functions, and a $16.9 million increase in personnel-related costs, mainly driven by an increase in average employee headcount.
We plan to continue increasing the capacity and enhancing the capability and reliability of our infrastructure to support user growth and increased activity on our platform.
We also expect that the amount of revenue generated from the sale of our advertising services on third party publishers’ websites, applications and other offerings will increase, which will also result in an increase in the amount of TAC that we incur.
As a result, we expect that cost of revenue, in particular TAC, will increase in absolute dollar amounts for the foreseeable future and vary in the near term from period to period as a percentage of revenue.
Research and Development Research and development expenses consist primarily of personnel-related costs, including salaries, benefits and stock-based compensation, for our engineers and other employees engaged in the research and development of our products and services.
In addition, research and development expenses include amortization of acquired intangible assets, allocated facilities and other supporting overhead costs.
## Table 2 ##
2015 Compared to 2014.
In 2015, research and development expenses increased by $115.1 million compared to 2014.
The increase was primarily attributable to an $87.0 million increase in personnel-related costs, mainly driven by an increase in compensation and recognition of stock-based compensation expense, and a $41.4 million increase in allocated facilities and other supporting overhead expenses due to the continued expansion of our real estate footprint and increase in support functions.
These increases were partially offset by a $13.3 million increase in the capitalization of costs associated with developing software for internal use.
As of December 31, 2015, we had $3.37 billion of federal and $1.34 billion of state net operating loss carryforwards available to reduce future taxable income.
These net operating loss carryforwards will begin to expire for federal income tax purposes and state income tax purposes in 2027 and 2016, respectively.
We also have research credit carryforwards of $188.2 million and $150.6 million for federal and state income tax purposes, respectively.
The federal research credit carryforward will begin to expire in 2027.
The state research credit carryforward has no expiration date.
Additionally, we have California Enterprise Zone credit carryforwards of $18.0 million which will begin to expire in 2023.
Utilization of the net operating loss carryforwards and research credit carryforwards may be subject to an annual limitation due to the ownership change limitations provided by the Internal Revenue Code of 1986, as amended, and similar state provisions.
Any annual limitation may result in the expiration of net operating losses and research credits before utilization.
Quarterly Results of Operations The following table sets forth our unaudited consolidated statement of operations data for each of the eight quarters in the period ended December 31, 2015.
The unaudited quarterly statement of operations data set forth below have been prepared on a basis consistent with our audited annual consolidated financial statements in this Annual Report on Form 10-K and include, in our opinion, all normal recurring adjustments necessary for a fair statement of the financial information contained in those statements.
Our historical results are not necessarily indicative of the results that may be expected in the future.
The following quarterly financial data should be read in conjunction with our audited consolidated financial statements and the related notes included elsewhere in this Annual Report on Form 10-K.
## Table 3 ##
Our environmental site activity was as follows:

<table><tr><td></td><td colspan="3">Year Ended December 31,</td><td rowspan="2">2014 to 2015 % Change</td><td rowspan="2">2013 to 2014 % Change</td></tr><tr><td></td><td>2015</td><td>2014</td><td>2013</td></tr><tr><td></td><td colspan="3">(in thousands)</td><td></td><td></td></tr><tr><td>Advertising services</td><td>$1,994,036</td><td>$1,255,688</td><td>$594,546</td><td>59%</td><td>111%</td></tr><tr><td>Data licensing and other</td><td>223,996</td><td>147,314</td><td>70,344</td><td>52%</td><td>109%</td></tr><tr><td>Total Revenue</td><td>$2,218,032</td><td>$1,403,002</td><td>$664,890</td><td>58%</td><td>111%</td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31,</td><td rowspan="2">2014 to 2015 % Change</td><td rowspan="2">2013 to 2014 % Change</td></tr><tr><td></td><td>2015</td><td>2014</td><td>2013</td></tr><tr><td></td><td colspan="3">(in thousands)</td><td></td><td></td></tr><tr><td>Cost of revenue</td><td>$729,256</td><td>$446,309</td><td>$266,718</td><td>63%</td><td>67%</td></tr><tr><td>Cost of revenue as a percentage of revenue</td><td>33%</td><td>32%</td><td>40%</td><td></td><td></td></tr></table>
<table><tr><td></td><td colspan="3">Year Ended December 31,</td><td rowspan="2">2014 to 2015 % Change</td><td rowspan="2">2013 to 2014 % Change</td></tr><tr><td></td><td>2015</td><td>2014</td><td>2013</td></tr><tr><td></td><td colspan="3">(in thousands)</td><td></td><td></td></tr><tr><td>Research and development</td><td>$806,648</td><td>$691,543</td><td>$593,992</td><td>17%</td><td>16%</td></tr><tr><td>Research and development as a percentage of revenue</td><td>36%</td><td>49%</td><td>89%</td><td></td><td></td></tr></table>
<table><tr><td></td><td colspan="8">Three Months Ended</td></tr><tr><td></td><td>Dec. 31, 2015</td><td>Sep. 30, 2015</td><td>Jun. 30, 2015</td><td>Mar. 31, 2015</td><td>Dec. 31, 2014</td><td>Sep. 30, 2014</td><td>Jun. 30, 2014</td><td>Mar. 31, 2014</td></tr><tr><td></td><td colspan="8">(Unaudited, in thousands, except per share data)</td></tr><tr><td>Consolidated Statement of Operations Data:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Revenue</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Advertising services</td><td>$640,680</td><td>$512,867</td><td>$452,278</td><td>$388,211</td><td>$432,001</td><td>$320,196</td><td>$277,440</td><td>$226,051</td></tr><tr><td>Data licensing and other</td><td>69,793</td><td>56,370</td><td>50,105</td><td>47,728</td><td>47,077</td><td>41,070</td><td>34,726</td><td>24,441</td></tr><tr><td>Total revenue</td><td>710,473</td><td>569,237</td><td>502,383</td><td>435,939</td><td>479,078</td><td>361,266</td><td>312,166</td><td>250,492</td></tr><tr><td>Costs and expenses<sup>-1</sup></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Cost of revenue</td><td>217,963</td><td>200,195</td><td>167,623</td><td>143,475</td><td>136,613</td><td>124,166</td><td>100,027</td><td>85,503</td></tr><tr><td>Research and development</td><td>210,058</td><td>207,937</td><td>198,907</td><td>189,746</td><td>181,715</td><td>183,342</td><td>177,095</td><td>149,391</td></tr><tr><td>Sales and marketing</td><td>277,189</td><td>208,797</td><td>201,948</td><td>183,557</td><td>203,599</td><td>164,015</td><td>140,261</td><td>106,235</td></tr><tr><td>General and administrative</td><td>72,442</td><td>57,545</td><td>64,909</td><td>65,777</td><td>55,304</td><td>51,174</td><td>44,694</td><td>38,734</td></tr><tr><td>Total costs and expenses</td><td>777,652</td><td>674,474</td><td>633,387</td><td>582,555</td><td>577,231</td><td>522,697</td><td>462,077</td><td>379,863</td></tr><tr><td>Loss from operations</td><td>-67,179</td><td>-105,237</td><td>-131,004</td><td>-146,616</td><td>-98,153</td><td>-161,431</td><td>-149,911</td><td>-129,371</td></tr><tr><td>Interest expense</td><td>-24,183</td><td>-25,239</td><td>-24,437</td><td>-24,319</td><td>-24,083</td><td>-6,079</td><td>-2,654</td><td>-3,102</td></tr><tr><td>Other income (expense), net</td><td>4,531</td><td>1,948</td><td>-695</td><td>9,125</td><td>571</td><td>-7,795</td><td>2,324</td><td>1,333</td></tr><tr><td>Loss before income taxes</td><td>-86,831</td><td>-128,528</td><td>-156,136</td><td>-161,810</td><td>-121,665</td><td>-175,305</td><td>-150,241</td><td>-131,140</td></tr><tr><td>Provision (benefit) for income taxes</td><td>3,405</td><td>3,162</td><td>-19,473</td><td>632</td><td>3,687</td><td>159</td><td>-5,599</td><td>1,222</td></tr><tr><td>Net loss</td><td>$-90,236</td><td>$-131,690</td><td>$-136,663</td><td>$-162,442</td><td>$-125,352</td><td>$-175,464</td><td>$-144,642</td><td>$-132,362</td></tr><tr><td>Net loss per share attributable to common stockholders:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Basic and diluted</td><td>$-0.13</td><td>$-0.20</td><td>$-0.21</td><td>$-0.25</td><td>$-0.20</td><td>$-0.29</td><td>$-0.24</td><td>$-0.23</td></tr><tr><td>Other Financial Information:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Adjusted EBITDA<sup>-2</sup></td><td>$191,418</td><td>$142,148</td><td>$120,188</td><td>$104,053</td><td>$141,490</td><td>$68,326</td><td>$54,131</td><td>$36,949</td></tr><tr><td>Non-GAAP net income<sup>-3</sup></td><td>$114,619</td><td>$66,984</td><td>$48,518</td><td>$46,508</td><td>$79,320</td><td>$6,972</td><td>$14,596</td><td>$183</td></tr></table>

Question: What is the sum of the Research and development in the years where Cost of revenue for Sep. 30 greater than 200000? (in thousand)
Answer: 806648