a(n) = A214938(2n).

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =46a(5) =207a(6) =977a(7) =4769a(8) =23872a(9) =121862a(10) =631958a(11) =3319923a(12) =17630692a(13) =94493713a(14) =510468519a(15) =2776629563a(16) =15194389388a(17) =83591476528a(18) =462062822648