Second differences are 2,2,1,2,1,1,2,1,1,1,2,1,1,1,1,2,1,1,1,1,1,2,.. (A035214).

Terms

a(0) =4a(1) =1a(2) =0a(3) =1a(4) =3a(5) =7a(6) =12a(7) =18a(8) =26a(9) =35a(10) =45a(11) =56a(12) =69a(13) =83a(14) =98a(15) =114a(16) =131a(17) =150a(18) =170a(19) =191a(20) =213a(21) =236a(22) =260a(23) =286a(24) =313a(25) =341a(26) =370a(27) =400a(28) =431a(29) =463