Number of ways of folding a strip of n labeled stamps.

Terms

a(0) =1a(1) =2a(2) =6a(3) =16a(4) =50a(5) =144a(6) =462a(7) =1392a(8) =4536a(9) =14060a(10) =46310a(11) =146376a(12) =485914a(13) =1557892a(14) =5202690a(15) =16861984a(16) =56579196a(17) =184940388a(18) =622945970a(19) =2050228360a(20) =6927964218a(21) =22930109884a(22) =77692142980a(23) =258360586368a(24) =877395996200