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a(2n-1) = n*a(2n-2), a(2n) = n*a(2n-1) + 1.
0
%I #2 May 16 2003 03:00:00
%S 1,2,4,9,27,82,328,1313,6565,32826,196956,1181737,8272159,57905114,
%T 463240912,3705927297,33353345673,300180111058,3001801110580,
%U 30018011105801,330198122163811,3632179343801922,43586152125623064
%N a(2n-1) = n*a(2n-2), a(2n) = n*a(2n-1) + 1.
%K nonn,easy
%O 1,2
%A buzzard(AT)math.berkeley.edu (Kevin Buzzard)