n! * Sum[k=floor(n/2)..n, 1/k].

Terms

a(0) =3a(1) =11a(2) =26a(3) =154a(4) =684a(5) =5508a(6) =35664a(7) =361296a(8) =3068640a(9) =37383840a(10) =392722560a(11) =5584394880a(12) =69878833920