a(n) = n*(n+1)*(5*n + 4)/6.

Terms

a(0) =0a(1) =3a(2) =14a(3) =38a(4) =80a(5) =145a(6) =238a(7) =364a(8) =528a(9) =735a(10) =990a(11) =1298a(12) =1664a(13) =2093a(14) =2590a(15) =3160a(16) =3808a(17) =4539a(18) =5358a(19) =6270a(20) =7280a(21) =8393a(22) =9614a(23) =10948a(24) =12400a(25) =13975a(26) =15678a(27) =17514a(28) =19488a(29) =21605