A067000 a(1) = 1; a(n) = Sum (n+k)!a(k)/(2k)!, k = 1..n-1.

1, 3, 27, 339, 5553, 112761, 2736099, 77252175, 2488315257, 90053238033, 3617791773723, 159761716507215, 7692231450102849, 401057043646065345, 22510943881422758739, 1353385233080839510335, 86771327488839208390473