a(n) = Sum_{k=0..n} 2^k * A000041(k) * A000009(n-k).

Terms

a(0) =1a(1) =3a(2) =11a(3) =36a(4) =118a(5) =351a(6) =1082a(7) =3093a(8) =8984a(9) =25164a(10) =70434a(11) =191808a(12) =525559a(13) =1404672a(14) =3755506a(15) =9906111a(16) =26057062a(17) =67703310a(18) =175745506a(19) =451392114a(20) =1157272780a(21) =2944110060a(22) =7468477985a(23) =18821686554a(24) =47337840114a(25) =118344795738a(26) =295156919969a(27) =732694232394