Second row of array defined in A056230.

Terms

a(0) =2a(1) =6a(2) =17a(3) =47a(4) =121a(5) =291a(6) =665a(7) =1467a(8) =3162a(9) =6718a(10) =14156a(11) =29702a(12) =62190a(13) =130060a(14) =271760a(15) =567488a(16) =1184917a(17) =2475907a(18) =5181798a(19) =10869647a(20) =22858188a(21) =48178441a(22) =101712259a(23) =214900119a(24) =454006064a(25) =958316150a(26) =2019797853a(27) =4248758319a(28) =8917387482a(29) =18670242203