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 A257337 #9 Apr 28 2015 11:03:32 %S A257337 4,9,13,23,16,35,24,41,30,47,40,53,42,55,54,71,60,77,72,85,82,93,88, %T A257337 101,96,109,102,121,116,125,122,129,130,141,136,147,146,157,154,167, %U A257337 160,179,166,177,172,185,184,201,190,207,200,213,206,221,214,225,224 %N A257337 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "4" arm. %C A257337 Place numbers 2,3,4,5 clockwise around a grid point (see illustration in "Spiral" link). Divide grid into four spiral arms. %C A257337 Extend each arm one step at a time, in rotation: first the 2 arm, then the 3 arm, then the 4 arm, then the 5 arm, then the 2 arm, etc. %C A257337 Rule for extending: next term in arm is smallest number such that each cell in the grid is relatively prime to its four (N,S,E,W) neighbors. Every term in the entire grid must be different. %C A257337 The four arms are A257335, A257336, A257337, A257338. %C A257337 Conjecture: every number > 1 appears in one of the four arms. %H A257337 Lars Blomberg, <a href="/A257337/b257337.txt">Table of n, a(n) for n = 1..10000</a> %H A257337 Popular Computing (Calabasas, CA), <a href="/A257321/a257321.png">Problem 146: Gcd</a>, Vol. 4 (No. 45, Dec 1976), page PC45-4. %H A257337 N. J. A. Sloane, <a href="/A257335/a257335.png">Spiral showing initial terms of A257335-A257338</a> %Y A257337 Cf. A064413, A257321-A257340. %K A257337 nonn %O A257337 1,1 %A A257337 _N. J. A. Sloane_, Apr 21 2015 %E A257337 Corrected a(4)-a(9) and more terms from _Lars Blomberg_, Apr 28 2015