# Math Help - Prove that, for odd...

1. ## Prove that, for odd...

(Note that pi should be taken as meaning p sub i. I don't know how to do formatting with this, and when I try, it removes it.)

Prove that, for odd pi, we have ∑((pi-1)/2) is congruent to ((pi)-1)/2 mod 2.

2. Hint : split up the $p_i$'s into two classes, according to whether they are $\equiv 1 \mod 4$ or $\equiv -1 \mod 4$.