A pyramidal number of the form n(n + 1)(4n - 1)/6, The first few are 1, 7, 22, 50, 95, ... (OEIS A002412). The generating function of the hexagonal pyramidal numbers is (x(3x + 1))/(x - 1)^4 = x + 7x^2 + 22x^3 + 50x^4 + ....