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 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