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 A270033 #23 Jun 29 2019 01:39:47
%S A270033 0,0,0,0,0,0,8,0,0,0,0,0,0,0,8,9,10,11,12,13,14,15,8,17,9,19,10,21,11,
%T A270033 23,8,25,13,9,14,29,10,31,8,11,17,35,9,37,19,13,8,41,14,43,11,9,23,47,
%U A270033 8,8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,8,10,10,10,10,10,10,10,8,11,11
%N A270033 a(n) is the smallest b for which the base-b representation of n contains at least one 7 (or 0 if no such base exists).
%C A270033 a(n) > 0 for n >= 15 since 17 is n written in base n-7.
%C A270033 The only perfect k-th powers (k >= 2) that can appear in this sequence are m^k with 2 <= m <= 7 and k a prime number.
%H A270033 Nathan Fox, <a href="/A270033/b270033.txt">Table of n, a(n) for n = 1..10000</a>
%t A270033 Table[SelectFirst[Range[8, 1200], DigitCount[n, #, 7] > 0 &], {n, 15, 120}] (* _Michael De Vlieger_, Mar 10 2016, Version 10 *)
%o A270033 (PARI) a(n) = if ((n<15) && (n!=7), 0, my(b=8); while(!vecsearch(Set(digits(n, b)), 7), b++); b); \\ _Michel Marcus_, Mar 10 2016
%Y A270033 Cf. A270027, A270028, A216194, A270029, A270030, A270031, A270032, A270034, A270035, A270043.
%K A270033 nonn,base
%O A270033 1,7
%A A270033 _Nathan Fox_, Mar 08 2016