+78 How many integers n, with 2≤n≤80, is ((n-1(n)(n+1))/8 equal to an integer?
listfor(n, 2, 80, (n*(n-1)*(n+1)) mod 8
=(6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0).
Note: Count ALL the zeros, and that is your answer!!!.
