a(n) = Sum_{k=0..n} T(n,k) * T(n,n+k), with T given by A027052.

Terms

a(0) =1a(1) =0a(2) =2a(3) =8a(4) =31a(5) =130a(6) =590a(7) =2798a(8) =13541a(9) =66724a(10) =332708a(11) =1673536a(12) =8479367a(13) =43218034a(14) =221383712a(15) =1138976166a(16) =5882112985a(17) =30479772624a(18) =158413903096a(19) =825556260636