a(n) = Sum_{k=0..2n}(k!*(2n - k)!)/(floor(k/2)!*floor((2n - k)/2)!)^2.

A327999

a(n) = Sum_{k=0..2n}(k!*(2n - k)!)/(floor(k/2)!*floor((2n - k)/2)!)^2.

Terms

    a(0) =1a(1) =5a(2) =28a(3) =160a(4) =896a(5) =4864a(6) =25600a(7) =131072a(8) =655360a(9) =3211264a(10) =15466496a(11) =73400320a(12) =343932928a(13) =1593835520a(14) =7314866176a(15) =33285996544a(16) =150323855360a(17) =674309865472

External references