a(n) = (n!)^2 * Sum_{k=0..floor(n/2)} 1 / ((n-2*k)! * 4^k * k!).

A346224

a(n) = (n!)^2 * Sum_{k=0..floor(n/2)} 1 / ((n-2*k)! * 4^k * k!).

Terms

    a(0) =1a(1) =1a(2) =3a(3) =15a(4) =114a(5) =1170a(6) =15570a(7) =256410a(8) =5103000a(9) =119773080a(10) =3264445800a(11) =101784097800

External references