A323960 Number of defective (binary) heaps on n elements with exactly four defects.

0, 8, 90, 1200, 12502, 111776, 1017060, 8762880, 77887920, 705522048, 6268548000, 60169824000, 543692724960, 5645713615360, 52992483226560, 596317674101760, 5840267078534400, 70071467744931840, 725037082634304000, 9448088175337574400, 100728713738898432000

Offset

4,2

Comments

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

Links

Alois P. Heinz, Table of n, a(n) for n = 4..200

Eric Weisstein's World of Mathematics, Heap

Wikipedia, Binary heap

Crossrefs

Column k=4 of A306343.

Cf. A056971.

Sequence in context: A247728 A056784 A166769 * A187667 A331512 A092956

Adjacent sequences: A323957 A323958 A323959 * A323961 A323962 A323963

Keyword

nonn

Author

Alois P. Heinz, Feb 09 2019

Status

approved