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