(2n)!/2^n.
1, 1, 6, 90, 2520, 113400, 7484400, 681080400, 81729648000, 12504636144000
2 seqfan posts
Mon Dec 14 08:28:00 CET 2009 [seqfan] Re: OEIS wiki user update
Sun Dec 13 10:37:54 CET 2009 [seqfan] Re: OEIS wiki user update
Index of A-numbers in seqfan: by ascending order
by month
by frequency
by keyword
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