a(n) = A027170(2n-1, n-2).

Terms

a(0) =7a(1) =43a(2) =185a(3) =740a(4) =2900a(5) =11293a(6) =43897a(7) =170608a(8) =663438a(9) =2582058a(10) =10058862a(11) =39225116a(12) =153111686a(13) =598228961a(14) =2339499161a(15) =9157016216a(16) =35870666366a(17) =140623656686a(18) =551684484386