Since, you are working modulo 17, you have that the product,Originally Posted bydooz33

15x14x13x12x11x10x9x8x7x6x5x4x3x2x1

Is the same as,

(-2)x(-3)x(-4)x(-5)x(-6)x(-7)x(-8)x8x7x6x5x4x3x2x1

Thus, you have, (multiply same numbers)

-1x4x9x16x25x36x49x64

Again, since you are working modulo 17 you have,

-1x4x(-8)x(-1)x(-8)x(2)x(-2)x(-4)

Thus, you have, (multiply same numbers)

1x16x64

Thus,

1x(-1)x(-4)

Thus,

4