Number of closed lambda-terms of size n with size 1 for the variables.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =4a(5) =13a(6) =42a(7) =139a(8) =506a(9) =1915a(10) =7558a(11) =31092a(12) =132170a(13) =580466a(14) =2624545a(15) =12190623a(16) =58083923a(17) =283346273a(18) =1413449148a(19) =7200961616a(20) =37425264180a(21) =198239674888