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 A160545 #57 Jun 10 2025 08:40:59
%S A160545 1,2,4,5,8,10,11,13,16,17,19,20,22,23,25,26,29,31,32,34,37,38,40,41,
%T A160545 43,44,46,47,50,52,53,55,58,59,61,62,64,65,67,68,71,73,74,76,79,80,82,
%U A160545 83,85,86,88,89,92,94,95,97,100,101,103,104,106,107,109,110,113,115,116
%N A160545 Numbers coprime to 21.
%C A160545 The asymptotic density of this sequence is 4/7. - _Amiram Eldar_, Oct 23 2020
%H A160545 Amiram Eldar, <a href="/A160545/b160545.txt">Table of n, a(n) for n = 1..10000</a>
%H A160545 <a href="/index/Rec#order_13">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,0,0,0,1,-1).
%F A160545 a(n+12) = a(n) + 21.
%F A160545 a(n) = 21*floor((n-1)/12)+f(n)+floor(f(n)/2)+2^floor(f(n)/4)+floor(((n+5) mod 12)/11)+floor(((n+3) mod 12)/11), where f(n)= (n-1) mod 12. - _Gary Detlefs_, Sep 22 2013
%F A160545 G.f.: x*(1+x+2*x^2+x^3+3*x^4+2*x^5+x^6+2*x^7+3*x^8+x^9+2*x^10+x^11+x^12) / ( (1+x) *(1+x^2) *(1+x+x^2) *(x^2-x+1) *(x^4-x^2+1) *(x-1)^2 ). - _R. J. Mathar_, Sep 27 2014
%t A160545 LinearRecurrence[{1,0,0,0,0,0,0,0,0,0,0,1,-1}, {1,2,4,5,8,10,11,13,16,17,19,20,22},67] (* _Ray Chandler_, Jul 15 2015 *)
%t A160545 Select[Range[100], CoprimeQ[21, #] &] (* _Amiram Eldar_, Oct 23 2020 *)
%o A160545 (Sage) [i for i in range(0,128) if gcd(21, i) == 1]
%Y A160545 Cf. A162699, A045572.
%K A160545 nonn,easy
%O A160545 1,2
%A A160545 _Zerinvary Lajos_, May 18 2009
%E A160545 Definition corrected by _Leroy Quet_, Jun 19 2009