a(n) = n*(6*n^2 + 15*n + 5)/2.

Terms

a(0) =0a(1) =13a(2) =59a(3) =156a(4) =322a(5) =575a(6) =933a(7) =1414a(8) =2036a(9) =2817a(10) =3775a(11) =4928a(12) =6294a(13) =7891a(14) =9737a(15) =11850a(16) =14248a(17) =16949a(18) =19971a(19) =23332a(20) =27050a(21) =31143a(22) =35629a(23) =40526a(24) =45852a(25) =51625a(26) =57863a(27) =64584a(28) =71806a(29) =79547