Truncated tetrahedral numbers: a(n) = (1/6)*(n+1)*(23*n^2 + 19*n + 6).

Terms

a(0) =1a(1) =16a(2) =68a(3) =180a(4) =375a(5) =676a(6) =1106a(7) =1688a(8) =2445a(9) =3400a(10) =4576a(11) =5996a(12) =7683a(13) =9660a(14) =11950a(15) =14576a(16) =17561a(17) =20928a(18) =24700a(19) =28900a(20) =33551a(21) =38676a(22) =44298a(23) =50440a(24) =57125a(25) =64376a(26) =72216a(27) =80668a(28) =89755a(29) =99500