# Problem 489: Common factors between two sequences
Let G(a, b) be the smallest non-negative integer n for which gcd(n3 + b,
(n + a)3 + b) is maximized. For example, G(1, 1) = 5 because gcd(n3 + 1,
(n + 1)3 + 1) reaches its maximum value of 7 for n = 5, and is smaller
for 0 ≤ n < 5. Let H(m, n) = Σ G(a, b) for 1 ≤ a ≤ m, 1 ≤ b ≤ n. You
are given H(5, 5) = 128878 and H(10, 10) = 32936544. Find H(18, 1900).