100 Followers Crossing Confusion !

Python:

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from math import factorial
print "Answer:", str(factorial(100)).count('1')

Whee

Python one-liner:

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import math
print(sum((1 if i=="1" else 0) for i in str(math.factorial(100))))
# prints 15

Mathematica Code :-

DigitCount[ $100!, 10, 1 ]$

Note :-

DigitCount[a,b,c] gives the number of digits c in the decimal representation of a in base b.