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

Author

Alois P. Heinz, Feb 09 2019

Keywords

• nonn

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.