Number of symmetric foldings of 2n+1 stamps.

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =28a(5) =89a(6) =287a(7) =935a(8) =3072a(9) =10157a(10) =33767a(11) =112736a(12) =377836a(13) =1270203a(14) =4282311a(15) =14470629a(16) =49005732a(17) =166261653a(18) =565055147a(19) =1923186472a(20) =6554868916a(21) =22367933148a(22) =76417819396a(23) =261335128098a(24) =894597454360