a(n) = A000045(n+6) - (n^2 + 4*n + 8).

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =15a(5) =36a(6) =76a(7) =148a(8) =273a(9) =485a(10) =839a(11) =1424a(12) =2384a(13) =3952a(14) =6505a(15) =10653a(16) =17383a(17) =28292a(18) =45964a(19) =74580a(20) =120905a(21) =195885a(22) =317231a(23) =513600a(24) =831360a(25) =1345536a(26) =2177521a(27) =3523733a(28) =5701983a(29) =9226500