2,2

Or number of permutations p of [n] having exactly two indices i in {1,...,n} such that p(i) > p(floor(i/2)).

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

Eric Weisstein's World of Mathematics, Heap

Wikipedia, Binary heap

Column k=2 of A306343.

Cf. A056971.

Sequence in context: A228341 A289576 A223832 * A306356 A188818 A047139

Adjacent sequences: A323955 A323956 A323957 * A323959 A323960 A323961

nonn

Alois P. Heinz, Feb 09 2019

approved