G.f.: C_{2,o}(y) - see p. 158 of Fan reference.

Terms

a(0) =3a(1) =14a(2) =57a(3) =235a(4) =969a(5) =4014a(6) =16695a(7) =69678a(8) =291609a(9) =1223060a(10) =5138488a(11) =21617717a(12) =91044538a(13) =383775880a(14) =1618868769a(15) =6832842691a(16) =28853864329a(17) =121894728098a(18) =515129513163