x!
factorial(x)
Gamma(1 + x)*polygamma(0, 1 + x)
/ 2 \ \polygamma (0, 1 + x) + polygamma(1, 1 + x)/*Gamma(1 + x)
/ 3 \ \polygamma (0, 1 + x) + 3*polygamma(0, 1 + x)*polygamma(1, 1 + x) + polygamma(2, 1 + x)/*Gamma(1 + x)