a(n) = Sum_{k=1..n} (P(n,k) + C(n,k)).

Terms

a(0) =0a(1) =2a(2) =7a(3) =22a(4) =79a(5) =356a(6) =2019a(7) =13826a(8) =109855a(9) =986920a(10) =9865123a(11) =108507158a(12) =1302065439a(13) =16926805676a(14) =236975181187