a(n) = A057863(n+1) * Sum_{k=0..n}(k! / (2*k+1)!!).

A279886

a(n) = A057863(n+1) * Sum_{k=0..n}(k! / (2*k+1)!!).

Terms

    a(0) =1a(1) =4a(2) =66a(3) =7200a(4) =6917400a(5) =72442188000

External references