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Number of permutations of 2 copies of 1..n with no element e[i>=2]<e[1+floor((i-2)/3)] (3-way heap)
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%I #3 Mar 31 2012 12:35:44

%S 1,3,12,108,1944,38718,994392,38570364,1447995258,79481475504,

%T 7085744965872

%N Number of permutations of 2 copies of 1..n with no element e[i>=2]<e[1+floor((i-2)/3)] (3-way heap)

%Y Simple 2-way heap A056971

%K nonn

%O 1,2

%A _R. H. Hardin_ May 17 2010