a(n) = Sum_{k=0..floor(n/2)} k! * 2^k * (n - 2*k)!.
A309618
a(n) = Sum_{k=0..floor(n/2)} k! * 2^k * (n - 2*k)!.
Terms
- a(0) =1a(1) =1a(2) =4a(3) =8a(4) =36a(5) =140a(6) =832a(7) =5376a(8) =42432a(9) =374592a(10) =3720960a(11) =40694784a(12) =486679296a(13) =6310114560a(14) =88168366080
External references
- oeis: A309618