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 A270029 #26 Jun 29 2019 01:39:30 %S A270029 0,0,4,0,0,0,4,5,6,7,4,4,4,4,4,5,5,5,4,6,6,6,4,7,7,7,4,4,4,4,4,9,5,9, %T A270029 4,10,10,5,4,5,5,5,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,17,5,5,4, %U A270029 5,5,7,4,7,5,7,4,4,4,4,4,5,5,5,4,5,5,5,4,5,5,5,4,4,4,4,4,5,5,5,4,26 %N A270029 a(n) is the smallest b for which the base-b representation of n contains at least one 3 (or 0 if no such base exists). %C A270029 a(n) > 0 for n >= 7 since 13 is n written in base n-3. %C A270029 The only perfect k-th powers (k >= 2) that can appear in this sequence are 2^k and 3^k with k a prime number. %H A270029 Nathan Fox, <a href="/A270029/b270029.txt">Table of n, a(n) for n = 1..10000</a> %t A270029 Table[SelectFirst[Range[4, 10^3], DigitCount[n, #, 3] > 0 &], {n, 7, 120}] (* _Michael De Vlieger_, Mar 10 2016, Version 10 *) %o A270029 (PARI) a(n) = if ((n<7) && (n!=3), 0, my(b=4); while(!vecsearch(Set(digits(n, b)), 3), b++); b); \\ _Michel Marcus_, Mar 10 2016 %Y A270029 Cf. A270027, A270028, A216194, A270030, A270031, A270032, A270033, A270034, A270035, A270039. %K A270029 nonn,base %O A270029 1,3 %A A270029 _Nathan Fox_, Mar 08 2016