a(1) = 1, a(n) = a(n-1) if n = 1 (mod 3), otherwise n*a(n-1).

A123144

a(1) = 1, a(n) = a(n-1) if n = 1 (mod 3), otherwise n*a(n-1).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =6a(4) =30a(5) =180a(6) =180a(7) =1440a(8) =12960a(9) =12960a(10) =142560a(11) =1710720a(12) =1710720a(13) =23950080a(14) =359251200a(15) =359251200a(16) =6107270400a(17) =109930867200a(18) =109930867200

External references