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 A324064 #7 Feb 16 2025 08:33:57
%S A324064 0,0,0,0,6,24,120,640,3150,16128,94080,614400,3801600,26864640,
%T A324064 203174400,1757184000,11783772000,95122227200,794598604800,
%U A324064 7821066240000,65767223808000,675845406720000,6895980748800000,83909612666880000,784784318782464000
%N A324064 Number of defective (binary) heaps on n elements where three ancestor-successor pairs do not have the correct order.
%C A324064 Or number of permutations p of [n] having exactly three pairs (i,j) in {1,...,n} X {1,...,floor(log_2(i))} such that p(i) > p(floor(i/2^j)).
%H A324064 Alois P. Heinz, <a href="/A324064/b324064.txt">Table of n, a(n) for n = 0..200</a>
%H A324064 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Heap.html">Heap</a>
%H A324064 Wikipedia, <a href="https://en.wikipedia.org/wiki/Binary_heap">Binary heap</a>
%H A324064 Wikipedia, <a href="https://en.wikipedia.org/wiki/Permutation">Permutation</a>
%Y A324064 Column k=3 of A306393.
%Y A324064 Cf. A056971.
%K A324064 nonn
%O A324064 0,5
%A A324064 _Alois P. Heinz_, Feb 13 2019