What is the remainder obtained when is divided by 14.
Notation : denotes the factorial notation. For example, .
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We note that n ! is divisible by 14 for n ≥ 7 . Therefore, we have:
n = 1 ∑ 2 0 0 n ! ≡ n = 1 ∑ 6 n ! (mod 14) ≡ ( 1 ! + 2 ! + 3 ! + 4 ! + 5 ! + 6 ! ) (mod 14) ≡ ( 1 ! + 2 ! + 3 ! + 4 ! + 0 ) (mod 14) ≡ ( 1 + 2 + 6 + 2 4 ) (mod 14) ≡ ( 1 + 2 + 6 + 1 0 ) (mod 14) ≡ 1 9 (mod 14) ≡ 5 (mod 14) Note that 5 ! + 6 ! = 7 ⋅ 5 ! which is divisible by 7