A323958 Number of defective (binary) heaps on n elements with exactly two defects.

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

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: A370200 A369315 A223832 * A306356 A188818 A047139

Adjacent sequences: A323955 A323956 A323957 * A323959 A323960 A323961

Keyword

nonn

Author

Alois P. Heinz, Feb 09 2019

Status

approved