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 A272431 #5 May 01 2016 08:56:04
%S A272431 1,1,1,7,9,31,403,757,2873,12607,333051,1592977,10684875,105031681,
%T A272431 697538325,8987362027,114294624633,975751249951,14157072527947,
%U A272431 124133073947209,2048876740991939,36859613739949357,443133109281574185,6166869485798451019
%N A272431 Number of ordered set partitions of {1,2,...,n} such that no part has the same size as any of its three immediate predecessors.
%H A272431 Alois P. Heinz, <a href="/A272431/b272431.txt">Table of n, a(n) for n = 0..100</a>
%Y A272431 Column k=3 of A261959.
%K A272431 nonn
%O A272431 0,4
%A A272431 _Alois P. Heinz_, Apr 29 2016