The sequence b[n] defined in A126939.

Terms

a(0) =0a(1) =2a(2) =4a(3) =10a(4) =36a(5) =116a(6) =356a(7) =1124a(8) =3558a(9) =11198a(10) =35274a(11) =111208a(12) =350478a(13) =1104474a(14) =3480856a(15) =10970176a(16) =34572858a(17) =108957948a(18) =343386454a(19) =1082198432a(20) =3410598912a(21) =10748664028a(22) =33874922056a(23) =106758413130a(24) =336454174998