Partial sum of centered tetrahedral numbers A005894.

Terms

a(0) =1a(1) =6a(2) =21a(3) =56a(4) =125a(5) =246a(6) =441a(7) =736a(8) =1161a(9) =1750a(10) =2541a(11) =3576a(12) =4901a(13) =6566a(14) =8625a(15) =11136a(16) =14161a(17) =17766a(18) =22021a(19) =27000a(20) =32781a(21) =39446a(22) =47081a(23) =55776a(24) =65625a(25) =76726a(26) =89181a(27) =103096a(28) =118581a(29) =135750