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A323958
Number of defective (binary) heaps on n elements with exactly two defects.
2
0, 2, 9, 48, 250, 1200, 5922, 34160, 185460, 1201920, 6837600, 49680576, 314028000, 2611065600, 17913619680, 162456519680, 1235053617600, 12593800627200, 99016069824000, 1062491684981760, 9425603347776000, 114292447803494400, 1026754912019865600
OFFSET
2,2
COMMENTS
Or number of permutations p of [n] having exactly two indices i in {1,...,n} such that p(i) > p(floor(i/2)).
LINKS
Eric Weisstein's World of Mathematics, Heap
Wikipedia, Binary heap
CROSSREFS
Column k=2 of A306343.
Cf. A056971.
Sequence in context: A370200 A369315 A223832 * A306356 A188818 A047139
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Feb 09 2019
STATUS
approved