what is 2 to the 40 power

2^40 means 2*2*2* ...*2*2 with 40 factors (numbers to be multiplied). 

Remember that (a^b)^c = a^bc

We know that 2^10 = 1024, hence:

2^40 = 2^(10*4) = (2^10)^4 = 1024^4

you can calculate that on any calculator.

You can use the calculator at this site to find the answer to  2^40