>>58
mod 2 で
a[n] ≡ 1 -1 -0 ≡ 0

mod 3 で
a[n] ≡ (-1)^n -0 -(-1)^n ≡ 0

n=2m+1 (m ≧ 1)の時
a[n] = (25^m)*5 -(9^m)*3 -(4^m)*2

mod 5 で
a[n] ≡ 0 - ((-1)^m)*(-2) - ((-1)^m)*2 ≡ 0