a(1) = 1; a(n) = Sum (n+k)!a(k)/(2k)!, k = 1..n-1.

A067000

a(1) = 1; a(n) = Sum (n+k)!a(k)/(2k)!, k = 1..n-1.

Terms

    a(0) =1a(1) =3a(2) =27a(3) =339a(4) =5553a(5) =112761a(6) =2736099a(7) =77252175a(8) =2488315257a(9) =90053238033

External references