(2*n)!-Sum ((-1)^(i+1)*binomial(n,i)*2^i*(2*i-1)!,i=1..n).

A006563

(2*n)!-Sum ((-1)^(i+1)*binomial(n,i)*2^i*(2*i-1)!,i=1..n).

Terms

    a(0) =1a(1) =0a(2) =44a(3) =-174a(4) =117256a(5) =-7589530a(6) =2965194588a(7) =-692238710870

External references