Maybe
(a^2 binomial(a + n + 1, b) + a^2 (-binomial(a + 1, b)) - b^2 c binomial(a + n + 1, b) + b^2 c binomial(a + 1, b) + b^2 binomial(a + n + 1, b) + b^2 n binomial(a + n + 1, b) - b^2 binomial(a + 1, b) + a b c binomial(a + n + 1, b) + 2 a c binomial(a + n + 1, b) - b c binomial(a + n + 1, b) + 2 c binomial(a + n + 1, b) + b c n binomial(a + n + 1, b) + 2 c n binomial(a + n + 1, b) - a b c binomial(a + 1, b) - 2 a c binomial(a + 1, b) + b c binomial(a + 1, b) - 2 c binomial(a + 1, b) - b n^2 binomial(a + n + 1, b) - n^2 binomial(a + n + 1, b) - 2 a b binomial(a + n + 1, b) + a binomial(a …