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 A257331 #11 Apr 30 2015 20:04:24 %S A257331 5,6,19,8,35,43,16,53,67,45,79,55,89,91,69,113,36,131,63,139,75,44, %T A257331 111,50,173,52,185,58,123,68,215,74,229,235,241,251,253,265,277,275, %U A257331 287,80,307,295,317,165,331,213,323,78,349,195,367,225,371,365,397,249 %N A257331 Construct spiral of numbers on square grid as in Comments; sequence gives terms along the "5" arm. %C A257331 Place numbers 2,3,5,7 clockwise around a grid point (see illustrations in links). Divide grid into four spiral arms. %C A257331 Extend each arm one step at a time, in rotation: first the 2 arm, then the 3 arm, then the 5 arm, then the 7 arm, then the 2 arm, etc. %C A257331 Rule for extending: next term in arm is smallest number such that each cell in the grid is relatively prime to its eight neighbors. Every term in the entire grid must be different. %C A257331 The four arms are A257329, A257330, A257331, A257332. %C A257331 Conjecture: every number > 1 appears in one of the four arms. %H A257331 Lars Blomberg, <a href="/A257331/b257331.txt">Table of n, a(n) for n = 1..10000</a> %H A257331 Popular Computing (Calabasas, CA), <a href="/A257321/a257321.png">Problem 146: Gcd</a>, Vol. 4 (No. 45, Dec 1976), page PC45-4. %H A257331 N. J. A. Sloane, <a href="/A257321/a257321_1.png">Spirals showing initial terms of A257321-A257332</a> %Y A257331 Cf. A064413, A257321-A257340, A257347 (the union list). %K A257331 nonn %O A257331 1,1 %A A257331 _N. J. A. Sloane_, Apr 21 2015 %E A257331 More terms from _Lars Blomberg_, Apr 27 2015