a(2n-1) = n*a(2n-2), a(2n) = n*a(2n-1) + 1.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =27a(5) =82a(6) =328a(7) =1313a(8) =6565a(9) =32826a(10) =196956a(11) =1181737a(12) =8272159a(13) =57905114a(14) =463240912a(15) =3705927297a(16) =33353345673a(17) =300180111058