13 times triangular numbers.

Terms

a(0) =0a(1) =13a(2) =39a(3) =78a(4) =130a(5) =195a(6) =273a(7) =364a(8) =468a(9) =585a(10) =715a(11) =858a(12) =1014a(13) =1183a(14) =1365a(15) =1560a(16) =1768a(17) =1989a(18) =2223a(19) =2470a(20) =2730a(21) =3003a(22) =3289a(23) =3588a(24) =3900a(25) =4225a(26) =4563a(27) =4914a(28) =5278a(29) =5655