a(n) = A335703(2n+1).

Terms

a(0) =2a(1) =5a(2) =16a(3) =52a(4) =174a(5) =618a(6) =2300a(7) =8764a(8) =34038a(9) =133858a(10) =530876a(11) =2112904a(12) =8417830a(13) =33592910a(14) =134211556a(15) =536403988a(16) =2144322638