3n4−14n3+21n2−10n=(n−2)(n−1)n(3n−5)3n4−14n3+21n2−10n=(n−2)(n−1)n(3n−5) chia hết cho 3

Ta lại có 3n4−14n3+21n2−10n=(n−2)(n−1)n(3n−5)=(n−2)(n−1)n(3n+3−8)=3(n−2)(n−1)n(n+1)−8(n−2)(n−1)n3n4−14n3+21n2−10n=(n−2)(n−1)n(3n−5)=(n−2)(n−1)n(3n+3−8)=3(n−2)(n−1)n(n+1)−8(n−2)(n−1)n

chia hết cho 8. Mà (3, 8) = 1 nên chia hết cho 24