Number of foldings of n labeled stamps in which both end leaves are inwards.

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =10a(5) =40a(6) =156a(7) =546a(8) =1986a(9) =6716a(10) =23742a(11) =79472a(12) =277178a(13) =925588a(14) =3205896a(15) =10711486a(16) =36963722a(17) =123712788a(18) =426075994a(19) =1429030624a(20) =4916833424a(21) =16526958144a(22) =56840484232a(23) =191466923584a(24) =658460090994