a(n) = n! * Sum_{k=0..floor(n/3)} (n - 3*k)^k/6^k.
A356633
a(n) = n! * Sum_{k=0..floor(n/3)} (n - 3*k)^k/6^k.
Terms
- a(0) =1a(1) =1a(2) =2a(3) =6a(4) =28a(5) =160a(6) =1080a(7) =8540a(8) =78400a(9) =816480a(10) =9492000a(11) =122337600a(12) =1736380800a(13) =26930904000a(14) =453515462400
External references
- oeis: A356633