a(n) = n! * Sum_{k=0..floor(n/2)} k^(n - 2*k)/k!.
A345747
a(n) = n! * Sum_{k=0..floor(n/2)} k^(n - 2*k)/k!.
Terms
- a(0) =1a(1) =0a(2) =2a(3) =6a(4) =36a(5) =240a(6) =2280a(7) =27720a(8) =425040a(9) =7862400a(10) =171188640a(11) =4319330400a(12) =125199708480
External references
- oeis: A345747