Number of alternating full cycles on n letters.

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =3a(5) =10a(6) =39a(7) =173a(8) =882a(9) =5052a(10) =32163a(11) =225230a(12) =1720635a(13) =14240070a(14) =126917155a(15) =1211969509a(16) =12345020175a(17) =133604426410