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 A358129 #11 Nov 04 2022 07:32:46 %S A358129 0,1,2,3,4,5,6,7,8,9,20,11,22,10,24,13,25,16,23,14,26,15,28,17,30,12, %T A358129 33,18,27,19,32,40,29,31,42,36,21,34,50,41,35,44,37,45,38,46,39,47,53, %U A358129 48,55,49,52,43,56,70,51,60,57,61,54,63,58,64,59,66,71,62,73,68,72,65,74,69,77,90,75 %N A358129 Lexicographically earliest sequence of distinct nonnegative integers on a square spiral such that no number shares a digit with any of its four orthogonally adjacent neighbors. %C A358129 This sequence is similar to A358021 except here only the four orthogonally adjacent neighbors are considered. It is unknown if the sequence eventually terminates; if it does, it does so after more than 1.5 million terms. In that range on numerous occasions the only available number is one containing only the digit 7. For example a(862833) = 7...7, where there are forty-nine 7's. %H A358129 Scott R. Shannon, <a href="/A358129/a358129.png">Image of the first 500000 terms</a>. The values are scaled across the spectrum from red to violet, with the value ranges increasing towards the violet end to give more color weighting to the larger numbers. %e A358129 The square spiral begins: %e A358129 . %e A358129 . %e A358129 25--13--24--10--22 19 %e A358129 | | | %e A358129 16 4---3---2 11 27 %e A358129 | | | | | %e A358129 23 5 0---1 20 18 %e A358129 | | | | %e A358129 14 6---7---8---9 33 %e A358129 | | %e A358129 26--15--28--17--30--12 %e A358129 . %e A358129 a(10) = 20 as when the tenth cell is filled its two orthogonal neighbors use the digits 1 and 9, and 20 is the smallest unused number that does not contain either of those digits. %Y A358129 Cf. A358021, A358048, A344325, A344367, A354111, A343530. %K A358129 nonn,base %O A358129 0,3 %A A358129 _Scott R. Shannon_ and _Eric Angelini_, Oct 30 2022