a(n) = 2^(2*n+1) - binomial(2*n+1, n+1).

Terms

a(0) =1a(1) =5a(2) =22a(3) =93a(4) =386a(5) =1586a(6) =6476a(7) =26333a(8) =106762a(9) =431910a(10) =1744436a(11) =7036530a(12) =28354132a(13) =114159428a(14) =459312152a(15) =1846943453a(16) =7423131482a(17) =29822170718a(18) =119766321572a(19) =480832549478