a(n) = A047080(2*n+1, n+2).

Terms

a(0) =1a(1) =4a(2) =12a(3) =37a(4) =118a(5) =380a(6) =1229a(7) =3989a(8) =12987a(9) =42394a(10) =138709a(11) =454768a(12) =1493690a(13) =4913969a(14) =16189534a(15) =53407853a(16) =176397299a(17) =583242159a(18) =1930349545a(19) =6394665589a(20) =21201345460a(21) =70346920007a(22) =233581374587a(23) =776105485336