a(n) = n! * Sum_{k=0..floor(n/3)} (n/6)^k * binomial(n-2*k,k)/(n-2*k)!.

A362173

a(n) = n! * Sum_{k=0..floor(n/3)} (n/6)^k * binomial(n-2*k,k)/(n-2*k)!.

Terms

    a(0) =1a(1) =1a(2) =1a(3) =4a(4) =17a(5) =51a(6) =481a(7) =3676a(8) =18369a(9) =272917a(10) =3011201a(11) =21058236a(12) =427112401a(13) =6160655359a(14) =55380250017

External references