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 A337368 #15 Aug 30 2020 01:28:07 %S A337368 0,1,2,3456789,3,12,4,356789,24,5,306789,45,6,103789,7,102,8,45679,80, %T A337368 35679,9,1028,10,11,306798,13,42,14,20,13789,15,204,25,46,3589,467,16, %U A337368 20359,17,23,41,208,18,34567,19,34576,289,54,21,22,4056789,26,305789,36,145,206,27,3489,67,1389,70,112,30 %N A337368 Spiral on a 2D square lattice, one term per cell, starting at the origin with 0; the four integers forming any 2 X 2 square have all digits 0 through 9 (with duplicate digits allowed). %C A337368 This is defined to be the lexicographically earliest permutation of the nonnegative integers with this property. %H A337368 Jean-Marc Falcoz, <a href="/A337368/b337368.txt">Table of n, a(n) for n = 1..3907</a> %e A337368 The spiral starts with the 2 X 2 square 0,1,2,A and this square contains all the digits 0 through 9 at least once; the upper right 2 X 2 square (here) has the same property —— and so have all the 2 X 2 squares of the grid. %e A337368 . %e A337368 18———K——19———L——289—54———21——22 A = 3456789 %e A337368 | | B = 356789 %e A337368 208 9———G——10——11———H———13 4056789 C = 306789 %e A337368 | | | | D = 103789 %e A337368 41 F 4———B——24———5 42 26 E = 45679 %e A337368 | | | | | | F = 35679 %e A337368 23 80 12 0———1 C 14 305789 G = 1028 %e A337368 | | | | | | | H = 306798 %e A337368 17 E 3———A———2 45 20 36 I = 3589 %e A337368 | | | | . J = 20359 %e A337368 J 8——102——7———D———6 13789 . K = 34567 %e A337368 | | . L= 34576 %e A337368 16——467——I——46——25——204——15 . ... %Y A337368 Cf. A337115 %K A337368 base,nonn %O A337368 1,3 %A A337368 _Eric Angelini_ and _Jean-Marc Falcoz_, Aug 25 2020