a(n) = A081537(n)/A081535(n), with a(2) = 1 by convention.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =1a(6) =15a(7) =33a(8) =56a(9) =495a(10) =420a(11) =330a(12) =3960a(13) =3432a(14) =3003a(15) =2574a(16) =80080a(17) =1601145a(18) =1225224a(19) =1108536a(20) =1007760a(21) =912912a(22) =19399380a(23) =17612595a(24) =82372752a(25) =149978400a(26) =212469400a(27) =196846650a(28) =5354228880a(29) =4976687100