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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 (list; graph; refs; listen; history; text; internal format)
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

Alois P. Heinz, Table of n, a(n) for n = 2..200

Eric Weisstein's World of Mathematics, Heap

Wikipedia, Binary heap

CROSSREFS

Column k=2 of A306343.

Cf. A056971.

Sequence in context: A228341 A289576 A223832 * A306356 A188818 A047139

Adjacent sequences:  A323955 A323956 A323957 * A323959 A323960 A323961

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Feb 09 2019

STATUS

approved

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Last modified June 6 04:15 EDT 2020. Contains 334859 sequences. (Running on oeis4.)