a(n) = 2*F(2*n+1) + 4*F(n+1)*F(n-1) for n > 0, with a(0) = 0 and F(n) = A000045(n).

Terms

a(0) =0a(1) =4a(2) =18a(3) =38a(4) =108a(5) =274a(6) =726a(7) =1892a(8) =4962a(9) =12982a(10) =33996a(11) =88994a(12) =232998a(13) =609988a(14) =1596978a(15) =4180934a(16) =10945836a(17) =28656562a(18) =75023862a(19) =196415012a(20) =514221186a(21) =1346248534a(22) =3524524428a(23) =9227324738a(24) =24157449798a(25) =63245024644a(26) =165577624146a(27) =433487847782