Find the remainder when 1 ! + 2 ! + 3 ! + ⋯ + 2 0 1 6 ! is divided by 12.
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You got it so easy! Nice +1
We know n ! = ( n ) × ( n − 1 ) × ( n − 2 ) × . . . × ( 2 ) × ( 1 ) That means, for n ≥ m , n ! is divisible by m, as n! contains m in it. For example, 3! = 3 × 2 × 1 = 6 , if m = 2, then 3! is divisible by 2, 3!/2 = 6/2 = 3 Using the above fact, we now gonna apply that in here. Taking n as 1 to 2016, and m as 12. All the factorials ≥ 1 2 ! is divisible by 12 and leaves the remainder "0". Therefore the remainder of 1! + 2! + ... + 2016! is when Sum-of n! divided by 12 for all n ≤ 11 = > 1 ! + 2 ! + 3 ! + 4 ! + . . . + 1 1 ! = 4 3 9 5 4 7 1 3 = > 1 ! + 2 ! + 3 ! + 4 ! + . . . + 1 1 ! = 1 2 ∗ 3 6 6 2 8 9 2 + 9
Therefore the remainder is 9.
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All numbers greater than 3 ! are divisible by 1 2 . So remainder is 1 ! + 2 ! + 3 ! = 1 + 2 + 6 = 9 .