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 A303783 #11 Dec 01 2019 22:28:28 %S A303783 1,10,2,11,3,14,4,19,5,20,6,21,7,24,8,29,9,30,100,12,101,13,104,15, %T A303783 109,16,110,17,111,18,114,22,119,23,120,25,121,26,124,27,129,28,130, %U A303783 31,131,32,134,33,139,34,140,35,141,36,144,37,149,38,150,39,151,40,154,41,159,42,160,43,161,44,164,45,169,46,170,47 %N A303783 Lexicographically earliest sequence of distinct terms such that what emerges from the mask is a square (see the Comment section for the mask explanation). %C A303783 For any pair of contiguous terms, one of the terms uses fewer digits than the other. This term is called the mask. Put the mask on the other term, starting from the left. What is not covered by the mask forms a square number. %C A303783 The sequence starts with a(1) = 1 and is always extended with the smallest integer not yet present that doesn't lead to a contradiction. %C A303783 This sequence is a permutation of the integers > 0, as all integers will appear at some point, either as mask or masked. %H A303783 Jean-Marc Falcoz, <a href="/A303783/b303783.txt">Table of n, a(n) for n = 1..10001</a> %e A303783 In the pair (1,10), 1 is the mask; 0 emerges and is a square; %e A303783 in the pair (10,2), 2 is the mask; 0 emerges and is a square; %e A303783 in the pair (2,11), 2 is the mask; 1 emerges and is a square; %e A303783 in the pair (11,3), 3 is the mask; 1 emerges and is a square; %e A303783 ... %e A303783 in the pair (11529,2018), 2018 is the mask; 9 emerges and is a square; %e A303783 etc. %Y A303783 Cf. A303782 (same idea with primes), A303784 (with even numbers), A303785 (with odd numbers), A303786 (rebuilds the sequence itself term by term). %K A303783 nonn,base %O A303783 1,2 %A A303783 _Eric Angelini_ and _Jean-Marc Falcoz_, Apr 30 2018