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 A271213 #8 Jun 02 2025 12:17:30
%S A271213 1,1,3,14,104,976,11616,161472,2582016,46451712,929003520,20437463040,
%T A271213 490498375680,12752940072960,357082301399040,10712468463943680,
%U A271213 342798990185594880,11655165645170933760,419585963202371911680,15944266600833991311360,637770664032408384307200
%N A271213 a(n) = 2^(n-2) * (n! + floor(n/2)!).
%C A271213 a(n) is the number of rearrangement patterns, i.e., the number of rearrangement map equivalence classes.
%D A271213 J. Burns, Counting a Class of Signed Permutations and Chord Diagrams related to DNA Rearrangement, Preprint.
%H A271213 J. Burns, <a href="http://jtburns.myweb.usf.edu/tables/rearrangement_maps.html">Table of Rearrangement Maps and Patterns for n = 1, 2, and 3</a>.
%F A271213 a(n)=2^(n-2)*(n!+floor(n/2)!)
%F A271213 a(n)~(pi*n/8)^(1/2) (2n/e)^n
%e A271213 For n=1 the a(1)=1 solution is the equivalence class {+1,-1}.For n=2 the a(2)=3 solutions are the equivalence classes {+1+2, -2-1}, {+1-2, +2-1, -2+1, -1+2}, and {+2+1, -1-2}
%t A271213 Table[2^(n-2)*(n!+Floor[n/2]!),{n,10}]
%Y A271213 Partition of A000165 into equivalence classes.
%Y A271213 Cf. A271214, A271216, A271217.
%K A271213 nonn,easy
%O A271213 0,3
%A A271213 _Jonathan Burns_, Apr 02 2016