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 A327091 #12 Sep 16 2019 00:58:50
%S A327091 0,1,5,36,264,2335,23609,272880,3543360,51123511,811313945,
%T A327091 14045781456,263429150544,5320671461575,115141595216009,
%U A327091 2657827340717760,65185383511024320,1692767331624879031,46400793659613081785,1338843898122140977776,40562412499251225624624
%N A327091 Number of chiral pairs of length n words with integer entries that cover an initial interval of positive integers.
%C A327091 If the word is achiral, i.e., the same as its reverse, we ignore it. If different from its reverse, we count it and its reverse as a chiral pair.
%H A327091 Andrew Howroyd, <a href="/A327091/b327091.txt">Table of n, a(n) for n = 1..200</a>
%F A327091 a(n) = Sum_{k=1..n} (k!/2) * (Stirling2(n, k) - Stirling2(ceiling(n/2), k)).
%e A327091 a(3) = 5 because there are the following chiral pairs of words:
%e A327091 112/211, 122/221,
%e A327091 123/321, 132/231, 213/312.
%o A327091 (PARI) a(n) = {sum(k=1, n, k! * (stirling(n, k, 2) - stirling((n+1)\2, k, 2)) / 2)}
%Y A327091 Row sums of A305622.
%K A327091 nonn
%O A327091 1,3
%A A327091 _Andrew Howroyd_, Sep 13 2019