a(n) = n!*2^(n-1)/Product_{k=1..n} tau(k) where tau = A000005.

A074740

a(n) = n!*2^(n-1)/Product_{k=1..n} tau(k) where tau = A000005.

Terms

    a(0) =1a(1) =2a(2) =6a(3) =16a(4) =80a(5) =240a(6) =1680a(7) =6720a(8) =40320a(9) =201600a(10) =2217600a(11) =8870400a(12) =115315200a(13) =807206400a(14) =6054048000a(15) =38745907200a(16) =658680422400

External references