Calculate the last 2 digits of the sum : S=1!+2!+3!+...+2015! (n!=1*2*3*...*n) (?)

1 Answer
George C.
Jun 17, 2017

13

Explanation:

1!+2!+3!+4!+5!+6!+7!+8!+9!

=1+2+6+24+120+720+5040+40320+362880

=409113

Any larger factorial will have 2 trailing 0's, so will not affect the last two digits 13

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