This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A323959 #7 Feb 16 2025 08:33:57
%S A323959 0,3,28,250,1760,12502,82880,576060,4200960,29987760,239978112,
%T A323959 1744142400,15361632000,119854864800,1159352230400,9698664271680,
%U A323959 103688467983360,906866458156800,10282952826685440,97685444140416000,1224926383944806400,11906083013106585600
%N A323959 Number of defective (binary) heaps on n elements with exactly three defects.
%C A323959 Or number of permutations p of [n] having exactly three indices i in {1,...,n} such that p(i) > p(floor(i/2)).
%H A323959 Alois P. Heinz, <a href="/A323959/b323959.txt">Table of n, a(n) for n = 3..200</a>
%H A323959 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Heap.html">Heap</a>
%H A323959 Wikipedia, <a href="https://en.wikipedia.org/wiki/Binary_heap">Binary heap</a>
%Y A323959 Column k=3 of A306343.
%Y A323959 Cf. A056971.
%K A323959 nonn
%O A323959 3,2
%A A323959 _Alois P. Heinz_, Feb 09 2019