%I #6 Mar 30 2012 18:39:03
%S 3,28,320,4272,65632,1149312,22712832,501216000,12225264128,
%T 326574262272,9478749110272,296914161754112,9979741990993920,
%U 358151267772203008,13664955628675399680,552220995731872481280
%N a(n) = 2^(n-1)*sum(k=0,n,(n+k)!/k!^2).
%K easy,nonn
%O 1,1
%A _Benoit Cloitre_, Jul 31 2002
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