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 A047304 #40 Dec 31 2021 05:48:35
%S A047304 1,2,3,4,5,6,8,9,10,11,12,13,15,16,17,18,19,20,22,23,24,25,26,27,29,
%T A047304 30,31,32,33,34,36,37,38,39,40,41,43,44,45,46,47,48,50,51,52,53,54,55,
%U A047304 57,58,59,60,61,62,64,65,66
%N A047304 Numbers not divisible by 7.
%C A047304 Numbers that are congruent to {1, 2, 3, 4, 5, 6} mod 7. Different from A020658.
%C A047304 More generally the sequence of numbers not divisible by some fixed integer m >= 2 is given by a(n,m) = n - 1 + floor((n+m-2)/(m-1)). - _Benoit Cloitre_, Jul 11 2009
%C A047304 Complement of A008589. - _Reinhard Zumkeller_, Nov 30 2009
%H A047304 Ivan Panchenko, <a href="/A047304/b047304.txt">Table of n, a(n) for n = 1..200</a>
%H A047304 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,1,-1).
%F A047304 a(n) = n - 1 + floor((n+5)/6). - _Benoit Cloitre_, Jul 11 2009
%F A047304 A109720(a(n)) = 1; A082784(a(n)) = 0. - _Reinhard Zumkeller_, Nov 30 2009
%F A047304 G.f.: x*(1+x+x^2+x^3+x^4+x^5+x^6) / ( (1+x)*(1+x+x^2)*(x^2-x+1)*(x-1)^2 ). - _R. J. Mathar_, Oct 08 2011
%F A047304 Sum_{n>=1} (-1)^(n+1)/a(n) = (cot(Pi/7) + tan(Pi/14) - tan(3*Pi/14))*Pi/7. - _Amiram Eldar_, Dec 31 2021
%t A047304 Select[Table[n,{n,200}],Mod[#,7]!=0&] (* _Vladimir Joseph Stephan Orlovsky_, Feb 18 2011 *)
%t A047304 Drop[Range[70],{7,-1,7}] (* or *) LinearRecurrence[{1,0,0,0,0,1,-1},{1,2,3,4,5,6,8},60] (* _Harvey P. Dale_, Aug 01 2021 *)
%o A047304 (Sage) [i for i in range(67) if gcd(7,i) == 1] # _Zerinvary Lajos_, Apr 21 2009
%o A047304 (PARI) a(n)=n-1+floor((n+5)/6) \\ _Benoit Cloitre_, Jul 11 2009
%Y A047304 Cf. A008589, A020658, A082784, A109720.
%K A047304 nonn,easy
%O A047304 1,2
%A A047304 _N. J. A. Sloane_