Number of ways of folding a 2 X n strip of stamps.

Terms

a(0) =1a(1) =2a(2) =8a(3) =60a(4) =320a(5) =1980a(6) =10512a(7) =60788a(8) =320896a(9) =1787904a(10) =9381840a(11) =51081844a(12) =266680992a(13) =1429703548a(14) =7432424160a(15) =39409195740a(16) =204150606976