Consider the following series written in form of a decimal
Find the digit in the place after the decimal point.
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First, we have that
9 1 = 0 , 1 1 1 1 1 1 . . . 9 9 1 = 0 , 0 1 0 1 0 1 . . . 9 9 9 1 = 0 , 0 0 1 0 0 1 . . . 9 9 9 9 1 = 0 , 0 0 0 1 0 0 0 1 . . . . . . . . .
So clearly the digit in the place will be equal to the number of factors of that number.
Now to calculate what is the number of factors of 2 0 1 4 , before we need the prime representation 2 0 1 4 = 2 x 1 9 x 5 3 .
So we use the function d ( 2 0 1 4 ) = d ( 2 ⋅ 1 9 ⋅ 5 3 ) = 8 .
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N o t e :
If we have a number n = a 1 k 1 a 2 k 2 a 3 k 3 . . . a n n n , the number of factor of n is ( k 1 + 1 ) ( k 2 + 1 ) ( k 3 + 1 ) . . . ( k n + 1 ) .