a(n) = (n!)^2 * Sum_{k=0..n} 2^(n-k) / (k!)^2.
A336804
a(n) = (n!)^2 * Sum_{k=0..n} 2^(n-k) / (k!)^2.
Terms
- a(0) =1a(1) =3a(2) =25a(3) =451a(4) =14433a(5) =721651a(6) =51958873a(7) =5091969555a(8) =651772103041
External references
- oeis: A336804
A336804
a(n) = (n!)^2 * Sum_{k=0..n} 2^(n-k) / (k!)^2.