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

Author

Alois P. Heinz, Feb 09 2019

Keywords

• nonn

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.