a(n) = T(n,n+3), array T as in A047130.

Terms

a(0) =1a(1) =4a(2) =14a(3) =48a(4) =179a(5) =656a(6) =2394a(7) =8744a(8) =32791a(9) =123188a(10) =463211a(11) =1744076a(12) =6632688a(13) =25303978a(14) =96699766a(15) =370030836a(16) =1422210560a(17) =5479757300a(18) =21147107145a(19) =81707846148a(20) =316422360163