a(n) is the (n+1)st (n+2)-gonal number.

Terms

a(0) =1a(1) =3a(2) =9a(3) =22a(4) =45a(5) =81a(6) =133a(7) =204a(8) =297a(9) =415a(10) =561a(11) =738a(12) =949a(13) =1197a(14) =1485a(15) =1816a(16) =2193a(17) =2619a(18) =3097a(19) =3630a(20) =4221a(21) =4873a(22) =5589a(23) =6372a(24) =7225a(25) =8151a(26) =9153a(27) =10234a(28) =11397a(29) =12645