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

A356328

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

Terms

    a(0) =1a(1) =1a(2) =1a(3) =1a(4) =5a(5) =21a(6) =61a(7) =281a(8) =2521a(9) =15625a(10) =84841a(11) =971521a(12) =10646461a(13) =83366141a(14) =962405445a(15) =15445935961a(16) =181502928881

External references