Pseudo-involutory Riordan companion of 1 + 2*x*M(x), where M(x) is the g.f. of A001006.

Terms

a(0) =1a(1) =0a(2) =0a(3) =2a(4) =0a(5) =6a(6) =8a(7) =24a(8) =60a(9) =148a(10) =396a(11) =1026a(12) =2744a(13) =7350a(14) =19872a(15) =54102a(16) =148104a(17) =407682a(18) =1127328a(19) =3130542a(20) =8726256a(21) =24407634a(22) =68482776a(23) =192698124a(24) =543642476a(25) =1537443024a(26) =4357677516a(27) =12376868254a(28) =35221087656a(29) =100409367690