a(n) = ((n+3)!/2)*Sum_{k=1..n} (-1)^(k+1)/(k+3).

A024189

a(n) = ((n+3)!/2)*Sum_{k=1..n} (-1)^(k+1)/(k+3).

Terms

    a(0) =3a(1) =3a(2) =78a(3) =186a(4) =4008a(5) =15912a(6) =340560a(7) =1931760a(8) =43139520a(9) =321312960a(10) =7611891840a(11) =70589232000

External references