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%I #3 Mar 30 2012 16:49:18
%S 1,3,27,339,5553,112761,2736099,77252175,2488315257,90053238033,
%T 3617791773723,159761716507215,7692231450102849,401057043646065345,
%U 22510943881422758739,1353385233080839510335,86771327488839208390473
%N a(1) = 1; a(n) = Sum (n+k)!a(k)/(2k)!, k = 1..n-1.
%Y Cf. A007683.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Feb 16 2002
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