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 A323958 #7 Feb 16 2025 08:33:57
%S A323958 0,2,9,48,250,1200,5922,34160,185460,1201920,6837600,49680576,
%T A323958 314028000,2611065600,17913619680,162456519680,1235053617600,
%U A323958 12593800627200,99016069824000,1062491684981760,9425603347776000,114292447803494400,1026754912019865600
%N A323958 Number of defective (binary) heaps on n elements with exactly two defects.
%C A323958 Or number of permutations p of [n] having exactly two indices i in {1,...,n} such that p(i) > p(floor(i/2)).
%H A323958 Alois P. Heinz, <a href="/A323958/b323958.txt">Table of n, a(n) for n = 2..200</a>
%H A323958 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Heap.html">Heap</a>
%H A323958 Wikipedia, <a href="https://en.wikipedia.org/wiki/Binary_heap">Binary heap</a>
%Y A323958 Column k=2 of A306343.
%Y A323958 Cf. A056971.
%K A323958 nonn
%O A323958 2,2
%A A323958 _Alois P. Heinz_, Feb 09 2019