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 A257334 #13 Apr 28 2015 11:03:03 %S A257334 3,2,5,4,7,8,9,11,13,6,17,10,19,14,23,12,25,16,29,15,31,22,21,20,37, %T A257334 18,35,24,41,26,27,28,43,32,33,34,39,38,45,44,47,30,49,36,53,40,51,46, %U A257334 55,42,59,48,61,50,57,52,63,58,65,54,67,56,69,71,60,73,62 %N A257334 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "3" arm. %C A257334 Place numbers 2,3,4,5 clockwise around a grid point (see illustration in "Spiral" link). Divide grid into four spiral arms. %C A257334 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 A257334 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. Inside an arm, the terms must be distinct. %C A257334 Repetitions between arms are permitted. %C A257334 The "2" arm is A257333, the "3" arm is the present sequence (A257334). The "4" arm begins 4,3,2,5, and thereafter agrees with the "2" arm. The "5" arm begins 5,2,3,4, and thereafter agrees with the "3" arm. %H A257334 Lars Blomberg, <a href="/A257334/b257334.txt">Table of n, a(n) for n = 1..10000</a> %H A257334 Popular Computing (Calabasas, CA), <a href="/A257321/a257321.png">Problem 146: Gcd</a>, Vol. 4 (No. 45, Dec 1976), page PC45-4. %H A257334 N. J. A. Sloane, <a href="/A257333/a257333_1.png">Spiral showing initial terms of A257333-A257334</a> %Y A257334 Cf. A064413, A257321-A257340. %K A257334 nonn %O A257334 1,1 %A A257334 _N. J. A. Sloane_, Apr 21 2015 %E A257334 Corrected a(25), a(29), a(30), a(32) and more terms from _Lars Blomberg_, Apr 28 2015