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 A298425 #13 Jan 22 2018 03:05:16
%S A298425 1,2,3,4,5,6,7,8,9,100,10,11,12,13,14,15,16,17,18,19,1000,20,21,22,23,
%T A298425 24,25,26,27,28,1001,29,101,30,31,32,33,34,35,36,37,1002,38,102,39,
%U A298425 103,40,41,42,43,44,45,46,1003,47,104,48,105,49,1004,50,51,52
%N A298425 Lexicographically earliest sequence of distinct positive terms such that, for any n> 0, Sum_{k = 1..n} 10^(n-k) * a(k) can be computed without carry in decimal base.
%C A298425 More informally: write the terms in decimal under each other, right-justified; the digits on each diagonal in upwards direction sum at most to 9.
%C A298425 See also A298359 for a similar sequence.
%H A298425 Rémy Sigrist, <a href="/A298425/b298425.txt">Table of n, a(n) for n = 1..1380</a>
%H A298425 Rémy Sigrist, <a href="/A298425/a298425.gp.txt">PARI program for A298425</a>
%H A298425 Rémy Sigrist, <a href="/A298425/a298425.png">Logarithmic scatterplot of a(n) for n = 1..5000</a> (with powers of 10 highlighted)
%H A298425 Rémy Sigrist, <a href="/A298425/a298425_1.png">logarithmic scatterplot of a(n) for n = 1..5000 and a(n) < 10^20</a>
%e A298425 The first 25 terms, alongside 10^(25-n) * a(n), are:
%e A298425 n a(n) 10^(25-n) * a(n)
%e A298425 -- ---- -------------------------
%e A298425 1 1 1000000000000000000000000
%e A298425 2 2 200000000000000000000000
%e A298425 3 3 30000000000000000000000
%e A298425 4 4 4000000000000000000000
%e A298425 5 5 500000000000000000000
%e A298425 6 6 60000000000000000000
%e A298425 7 7 7000000000000000000
%e A298425 8 8 800000000000000000
%e A298425 9 9 90000000000000000
%e A298425 10 100 100000000000000000
%e A298425 11 10 1000000000000000
%e A298425 12 11 110000000000000
%e A298425 13 12 12000000000000
%e A298425 14 13 1300000000000
%e A298425 15 14 140000000000
%e A298425 16 15 15000000000
%e A298425 17 16 1600000000
%e A298425 18 17 170000000
%e A298425 19 18 18000000
%e A298425 20 19 1900000
%e A298425 21 1000 10000000
%e A298425 22 20 20000
%e A298425 23 21 2100
%e A298425 24 22 220
%e A298425 25 23 23
%e A298425 The terms on the third column can be summed without carry in decimal base.
%o A298425 (PARI) See Links section.
%Y A298425 Cf. A298359.
%K A298425 nonn,base
%O A298425 1,2
%A A298425 _Rémy Sigrist_, Jan 19 2018