A323960 - OEIS

%I #6 Feb 09 2019 21:17:37

%S 0,8,90,1200,12502,111776,1017060,8762880,77887920,705522048,

%T 6268548000,60169824000,543692724960,5645713615360,52992483226560,

%U 596317674101760,5840267078534400,70071467744931840,725037082634304000,9448088175337574400,100728713738898432000

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

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

%H Alois P. Heinz, <a href="/A323960/b323960.txt">Table of n, a(n) for n = 4..200</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Heap.html">Heap</a>

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Binary_heap">Binary heap</a>

%Y Column k=4 of A306343.

%Y Cf. A056971.

%K nonn

%O 4,2

%A _Alois P. Heinz_, Feb 09 2019