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 A272573 #12 May 07 2016 00:25:08 %S A272573 1,2,3,4,5,6,7,4,6,8,5,9,8,10,2,11,3,10,11,12,13,9,12,7,13,14,1,11,13, %T A272573 15,9,16,14,7,16,17,15,1,16,18,7,17,19,20,1,17,18,19,9,21,3,20,10,22, %U A272573 4,15,21,23,5,22,23,10,21,6,22,24,25,2,14,22,25,26,3 %N A272573 Start a spiral of numbers on a hexagonal tiling, with the initial hexagon as a(1) = 1. a(n) is the smallest positive integer not equal to or previously adjacent to its neighbors. %C A272573 This is the hexagonal analog to A260643. %H A272573 Peter Kagey, <a href="/A272573/b272573.txt">Table of n, a(n) for n = 1..10000</a> %H A272573 Peter Kagey, <a href="/A272573/a272573.txt">Ruby program for computing sequence</a>. %e A272573 Illustration of a(1) through a(8) and a(13): %e A272573 | | | | | | | | | 8 9 5 %e A272573 | | 3 | 4 3 | 4 3 | 4 3 | 4 3 | 4 3 | | 4 3 8 %e A272573 1 | 1 2 | 1 2 | 1 2 | 5 1 2 | 5 1 2 | 5 1 2 | 5 1 2 | ... | 5 1 2 6 %e A272573 | | | | | 6 | 6 7 | 6 7 4 | | 6 7 4 %Y A272573 Cf. A047932, A260643. %K A272573 nonn %O A272573 1,2 %A A272573 _Peter Kagey_, May 03 2016