a(n) = ceiling(n*(n+1)*(n+2)/8).

Terms

a(0) =0a(1) =1a(2) =3a(3) =8a(4) =15a(5) =27a(6) =42a(7) =63a(8) =90a(9) =124a(10) =165a(11) =215a(12) =273a(13) =342a(14) =420a(15) =510a(16) =612a(17) =727a(18) =855a(19) =998a(20) =1155a(21) =1329a(22) =1518a(23) =1725a(24) =1950a(25) =2194a(26) =2457a(27) =2741a(28) =3045a(29) =3372