is divided by ?
What is the remainder when
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We can first write n 4 as: n 4 = 2 4 ( 4 n ) + 3 6 ( 3 n ) + 1 4 ( 2 n ) + ( 1 n ) in order to exploit the identity: n = 0 ∑ 2 0 1 4 ( k n ) ( n 2 0 1 4 ) = ( k 2 0 1 4 ) ⋅ 2 2 0 1 4 − k . Since 8 1 9 = 3 2 ⋅ 7 ⋅ 1 3 , we just have to compute the residue classes ( m o d 7 , 9 , 1 3 ) of: 2 4 ( 4 2 0 1 4 ) 2 2 0 1 0 + 3 6 ( 3 2 0 1 4 ) 2 2 0 1 1 + 1 4 ( 2 2 0 1 4 ) 2 2 0 1 2 + 2 0 1 4 ⋅ 2 2 0 1 3 . Since ϕ ( 1 3 ) = 2 ϕ ( 9 ) = 2 ϕ ( 6 ) , this is the same as calculating the residue classes ( m o d 7 , 9 , 1 3 ) of: 2 4 ( 4 2 0 1 4 ) 2 6 + 3 6 ( 3 2 0 1 4 ) 2 7 + 1 4 ( 2 2 0 1 4 ) 2 8 + 2 0 1 4 ⋅ 2 9 , or: ( 2 0 1 4 ⋅ 2 0 1 3 ⋅ 2 0 1 2 ⋅ 2 0 1 1 ) ⋅ 2 6 + 6 ( 2 0 1 4 ⋅ 2 0 1 3 ⋅ 2 0 1 2 ) ⋅ 2 7 + 7 ⋅ ( 2 0 1 4 ⋅ 2 0 1 3 ) ⋅ 2 8 + 2 0 1 4 ⋅ 2 9 . The last sum is just 2 ( m o d 9 ) , 5 ( m o d 7 ) , 0 ( m o d 1 3 ) , hence the answer is 2 9 9 by the chinese theorem.