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A324063
Number of defective (binary) heaps on n elements where two ancestor-successor pairs do not have the correct order.
2
0, 0, 0, 2, 6, 24, 100, 480, 1890, 8960, 47040, 288000, 1584000, 10644480, 74131200, 615014400, 3783780000, 29520691200, 230015385600, 2199674880000, 17239951872000, 172890685440000, 1660143513600000, 19778694414336000, 174145223476224000, 2007117934991769600
OFFSET
0,4
COMMENTS
Or number of permutations p of [n] having exactly two pairs (i,j) in {1,...,n} X {1,...,floor(log_2(i))} such that p(i) > p(floor(i/2^j)).
LINKS
Eric Weisstein's World of Mathematics, Heap
Wikipedia, Binary heap
Wikipedia, Permutation
CROSSREFS
Column k=2 of A306393.
Cf. A056971.
Sequence in context: A094012 A141253 A306672 * A078486 A352364 A129817
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Feb 13 2019
STATUS
approved