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 A273755 #14 Feb 16 2025 08:33:35 %S A273755 1,1,1,1,2,3,5,11,26,55,214,547,1802,6579,22446,77170,401150,1509788, %T A273755 7198829,36540168 %N A273755 Number of binary min heaps on [n] that give a max heap when reversed. %C A273755 Or number of binary max heaps on [n] that give a min heap when reversed. %H A273755 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Heap.html">Heap</a> %H A273755 Wikipedia, <a href="https://en.wikipedia.org/wiki/Binary_heap">Binary heap</a> %e A273755 a(4) = 2: 1234, 1324. %e A273755 a(5) = 3: 12345, 12435, 13245. %e A273755 a(6) = 5: 123456, 123546, 124356, 132456, 132546. %e A273755 a(7) = 11: 1234567, 1234657, 1235467, 1243567, 1243657, 1245367, 1253467, 1254367, 1324567, 1324657, 1325467. %Y A273755 Cf. A056971, A273754. %K A273755 nonn,more %O A273755 0,5 %A A273755 _Alois P. Heinz_, May 29 2016