Number of foldings of n labeled stamps in which leaf n is inwards.

Terms

a(0) =0a(1) =0a(2) =2a(3) =6a(4) =26a(5) =78a(6) =288a(7) =888a(8) =3130a(9) =9850a(10) =34112a(11) =108998a(12) =374636a(13) =1211046a(14) =4148816a(15) =13533796a(16) =46304730a(17) =152153758a(18) =520434552a(19) =1720325302a(20) =5885686496a(21) =19552190624a(22) =66927118548a(23) =223264746520a(24) =764725528072