"distribution date" ) .until the distribution date ( or earlier redemption or expiration of the rights ) , the rights will be traded with , and only with , the common stock .until a right is exercised , the right will not entitle the holder thereof to any rights as a stockholder .if any person or group becomes an acquiring person , each holder of a right , other than rights beneficially owned by the acquiring person , will thereafter have the right to receive upon exercise and payment of the purchase price that number of shares of common stock having a market value of two times the purchase price and , if the company is acquired in a business combination transaction or 50% ( 50 % ) or more of its assets are sold , each holder of a right will thereafter have the right to receive upon exercise and payment of the purchase price that number of shares of common stock of the acquiring company which at the time of the transaction will have a market value of two times the purchase price .at any time after any person becomes an acquiring person and prior to the acquisition by such person or group of 50% ( 50 % ) or more of the outstanding common stock , the board of directors of the company may cause the rights ( other than rights owned by such person or group ) to be exchanged , in whole or in part , for common stock or junior preferred shares , at an exchange rate of one share of common stock per right or one half of one-hundredth of a junior preferred share per right .at any time prior to the acquisition by a person or group of beneficial ownership of 15% ( 15 % ) or more of the outstanding common stock , the board of directors of the company may redeem the rights at a price of $ 0.01 per right .the rights have certain anti-takeover effects , in that they will cause substantial dilution to a person or group that attempts to acquire a significant interest in vertex on terms not approved by the board of directors .common stock reserved for future issuance at december 31 , 2005 , the company has reserved shares of common stock for future issuance under all equity compensation plans as follows ( shares in thousands ) : o .significant revenue arrangements the company has formed strategic collaborations with pharmaceutical companies and other organizations in the areas of drug discovery , development , and commercialization .research , development and commercialization agreements provide the company with financial support and other valuable resources for its research programs and for the development of clinical drug candidates , and the marketing and sales of products .collaborative research , development and commercialization agreements in the company's collaborative research , development and commercialization programs the company seeks to discover , develop and commercialize pharmaceutical products in conjunction with and supported by the company's collaborators .collaborative research and development arrangements may provide research funding over an initial contract period with renewal and termination options that .
[['common stock under stock and option plans', '17739'], ['common stock under the vertex purchase plan', '842'], ['common stock under the vertex 401 ( k ) plan', '270'], ['total', '18851']]
.

Question: what percent of the total common stock is under the vertex purchase plan?
Answer: 4.5%