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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.

A257340 Arrange numbers in a single clockwise spiral so that each number is relatively prime to its four (N,S,E,W) neighbors.

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%I A257340 #17 Apr 23 2015 23:15:24
%S A257340 1,2,3,4,5,6,7,8,9,10,11,13,12,17,15,14,19,16,23,18,25,22,21,20,27,26,
%T A257340 29,24,31,35,32,37,28,41,33,34,39,40,43,30,47,36,49,38,45,44,51,46,53,
%U A257340 42,55,48,59,50,57,61,52,63,58,65,54,67,69,56,71,62,73
%N A257340 Arrange numbers in a single clockwise spiral so that each number is relatively prime to its four (N,S,E,W) neighbors.
%C A257340 Start with 1; always choose smallest number which has not yet appeared.
%C A257340 It is conjectured that every number appears.
%H A257340 Reinhard Zumkeller, <a href="/A257340/b257340.txt">Table of n, a(n) for n = 1..10000</a>
%e A257340 .     |     -4 | -3 | -2 | -1 |  0 | +1 | +2 | +3 | +4 | +5
%e A257340 .  ---+--------+----+----+----+----+----+----+----+----+----
%e A257340 .     |
%e A257340 .     |   +------------------------------------------------
%e A257340 .  +4 |   | 83   68   75   74   81   70   87   76   85  ...
%e A257340 .  ---+   |    +---------------------------------------+
%e A257340 .  +3 |   | 66 | 49   38   45   44   51   46   53   42 |
%e A257340 .  ---+   |    |    +-----------------------------+    |
%e A257340 .  +2 |   | 79 | 36 | 25   22   21   20   27   26 | 55 |
%e A257340 .  ---+   |    |    |    +-------------------+    |    |
%e A257340 .  +1 |   | 64 | 47 | 18 |  7    8    9   10 | 29 | 48 |
%e A257340 .  ---+   |    |    |    |    +---------+    |    |    |
%e A257340 .   0 |   | 77 | 30 | 23 |  6 |  1    2 | 11 | 24 | 59 |
%e A257340 .  ---+   |    |    |    |    +----o    |    |    |    |
%e A257340 .  -1 |   | 60 | 43 | 16 |  5    4    3 | 13 | 31 | 50 |
%e A257340 .  ---+   |    |    |    +--------------+    |    |    |
%e A257340 .  -2 |   | 73 | 40 | 19   14   15   17   12 | 35 | 57 |
%e A257340 .  ---+   |    |    +------------------------+    |    |
%e A257340 .  -3 |   | 62 | 39   34   33   41   28   37   32 | 61 |
%e A257340 .  ---+   |    +----------------------------------+    |
%e A257340 .  -4 |   | 71   56   69   67   54   65   58   63   52 |
%e A257340 .  ---+   +--------------------------------------------+
%e A257340 .
%Y A257340 Cf. A064413, A257321-A257339.
%K A257340 nonn
%O A257340 1,2
%A A257340 _N. J. A. Sloane_, Apr 21 2015
%E A257340 More terms from _Jon E. Schoenfield_, Apr 23 2015