A figurate number of the form P_n^(4) = 1/6 n(n + 1)(2n + 1), corresponding to a configuration of points which form a square pyramid, is called a square pyramidal number (or sometimes, simply a pyramidal number). The first few are 1, 5, 14, 30, 55, 91, 140, 204, ... (OEIS A000330). The generating function for square pyramidal numbers is (x(x + 1))/(x - 1)^4 = x + 5x^2 + 14x^3 + 30x^4 + ....

pyramidal number | tetrahedral number