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 A210417 #22 Apr 18 2021 02:15:07 %S A210417 2,3,30,6,31,9,32,13,33,12,14,21,34,25,35,29,333,3333,36,38,42,300,47, %T A210417 301,52,302,57,303,59,63,66,304,71,305,76,306,81,307,86,308,91,309,96, %U A210417 310,102,311,108,312,113,117,313,119,126,314,130,133,134,136,139 %N A210417 List the positions of all digits 3 in the concatenation of all terms, not necessarily in order. This is the lexicographically earliest such sequence. %C A210417 See A210415 for comments, links, and code. %H A210417 Danny Rorabaugh, <a href="/A210417/b210417.txt">Table of n, a(n) for n = 1..1000</a> %e A210417 The sequence cannot start with 1 because the first digit is not 3. Let us start with 2: the second digit is equal to 3. So in the second position we have 3 and the third digit must be 3. Because 3 has been already used the minimum number starting with 3 is 30. And so on. %Y A210417 Cf. A210414, A210415, A210416, A210418, A210419, A210420, A210421, A210422, A210423. %K A210417 nonn,base %O A210417 1,1 %A A210417 _Paolo P. Lava_, Mar 26 2012 %E A210417 Name edited and a(30)-a(34) corrected by _Danny Rorabaugh_, Nov 30 2015