How do I find the closed form of the sum : -LSB- math -RSB- \ sum _ -LCB- k = 1 -RCB- ^ -LCB- n -RCB- -LRB- 3 -RRB- ^ k \ binom -LCB- n -RCB- -LCB- k -RCB- -LSB- / math -RSB- ?
How can I find the closed form of the sum -LSB- math -RSB- \ sum _ -LCB- k = 1 -RCB- ^ -LCB- n -RCB- -LCB- k -LRB- k-1 -RRB- -RCB- \ binom -LCB- n -RCB- -LCB- k -RCB- -LSB- / math -RSB- ?