Binomial transform of A000957.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =10a(5) =31a(6) =110a(7) =421a(8) =1686a(9) =6961a(10) =29392a(11) =126292a(12) =550360a(13) =2426503a(14) =10803802a(15) =48507844a(16) =219377950a(17) =998436793a(18) =4569488372a(19) =21016589074a(20) =97090411020a(21) =450314942683