a(n) = n! * Sum_{k=ceiling(n/2)..n} 1/k.

Terms

a(0) =1a(1) =3a(2) =5a(3) =26a(4) =94a(5) =684a(6) =3828a(7) =35664a(8) =270576a(9) =3068640a(10) =29400480a(11) =392722560a(12) =4546558080a(13) =69878833920a(14) =948550176000