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 A249102 #19 Nov 02 2017 23:11:39 %S A249102 0,2,3,4,5,6,14,16,17,18,19,20,21,23,24,25,26,27,28,30,31,32,33,34,35, %T A249102 37,38,39,40,41,42,44,45,46,47,48,98,100,101,102,103,104,112,114,115, %U A249102 116,117,118,119,121,122,123,124,125,126,128,129,130,131,132,133 %N A249102 Numbers with no 1's in base-7 expansion. %H A249102 G. C. Greubel, <a href="/A249102/b249102.txt">Table of n, a(n) for n = 1..5000</a> %e A249102 14_10 = 20_7, 16_10 = 22_10, 17_10 = 23_7. %e A249102 14 in base 7 is 20, which contains no 1s, so 14 is in the sequence. %e A249102 15 in base 7 is 21, which contains one 1, so 15 is not in the sequence. %e A249102 16 in base 7 is 22, so 16 is in the sequence. %t A249102 Select[Range[0, 200], FreeQ[IntegerDigits[#, 7], 1] &] (* Seidov *) %t A249102 Select[Range[0, 139], DigitCount[#, 7, 1] == 0 &] (* _Alonso del Arte_, Oct 26 2014 *) %o A249102 (PARI) fromdigits(v, b=10)=subst(Pol(v), 'x, b) \\ needed for gp < 2.63 or so %o A249102 a(n)=a(n)=fromdigits(apply(k->if(k, k+1, 0), digits(n, 6)),7) \\ _Charles R Greathouse IV_, Oct 30 2014 %Y A249102 Subsequence of A047306. Cf. A023721, A023725, A023729, A023733, A005823. This sequence has no terms in common with A016993. %K A249102 base,nonn %O A249102 1,2 %A A249102 _Zak Seidov_, Oct 21 2014