Question

I am currently trying out Project Euler and one of the question is calculate 2^1000, and count the number of digits. I can easily do it for 2^15 but the issue with 2^1000 is that when I calculate it, it’s given in scientific notation, so it’s hard to sum the digits.

import math

def power(x):
    y_p=1000*math.log(x,10.0)
    y=math.pow(10,y_p)
    return y

if __name__=="__main__":

    ans=power(2)
    a=str(ans)
    print a
    sum=0

    for i in a:
       if i == ".":
          print "encountered ."
       elif i == "e":
          break
       else:
          sum=sum+int(i)

    print sum

Answer 1

To calculate 2^1000 in Python use 2**1000. Using floating point functions like math.log and math.pow you are likely to get inaccurate results.

Now, here is how to do it:

l = str(2**1000)
digits = [int(digit) for digit in l]
print sum(digits)

The first line converts the number to a string in base 10 representation.The second line iterates on the characters and transforms the string to a list of digits. And the third prints their sum.