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A323960
Number of defective (binary) heaps on n elements with exactly four defects.
2
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
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
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Feb 09 2019
STATUS
approved