Convolution of A001654 and A007598.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =12a(5) =38a(6) =122a(7) =372a(8) =1119a(9) =3301a(10) =9624a(11) =27756a(12) =79380a(13) =225384a(14) =636061a(15) =1785639a(16) =4990116a(17) =13889618a(18) =38524238a(19) =106514652a(20) =293668923a(21) =807608137a(22) =2215854384a(23) =6066935640a(24) =16579195560a(25) =45226399440a(26) =123173004985a(27) =334955873739a(28) =909611388732