For how many integers n, with 2\le n\le80, is \displaystyle\frac{(n-1)(n)(n+1)}{8} equal to an integer?
Answer Choices
A. 10
B. 20
C. 59
D. 39
E. 49
For how many integers n, with 2\le n\le80, is \displaystyle\frac{(n-1)(n)(n+1)}{8} equal to an integer?
Answer Choices
A. 10
B. 20
C. 59
D. 39
E. 49