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 A109015 #29 Dec 01 2021 05:17:41
%S A109015 12,1,2,3,4,1,6,1,4,3,2,1,12,1,2,3,4,1,6,1,4,3,2,1,12,1,2,3,4,1,6,1,4,
%T A109015 3,2,1,12,1,2,3,4,1,6,1,4,3,2,1,12,1,2,3,4,1,6,1,4,3,2,1,12,1,2,3,4,1,
%U A109015 6,1,4,3,2,1,12,1,2,3,4,1,6,1,4,3,2,1,12,1,2,3,4,1,6,1,4,3,2,1,12,1,2
%N A109015 a(n) = gcd(n,12).
%C A109015 Periodic, with period = 12. - _Harvey P. Dale_, Dec 20 2018
%H A109015 <a href="/index/Rec#order_12">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,0,0,0,1).
%F A109015 a(n) = 1 + [2|n] + 2*[3|n] + 2*[4|n] + 2*[6|n] + 4*[12|n], where [x|y] = 1 when x divides y, 0 otherwise.
%F A109015 a(n) = a(n-12).
%F A109015 Multiplicative with a(p^e, 12) = gcd(p^e, 12). - _David W. Wilson_, Jun 12 2005
%F A109015 Dirichlet g.f.: zeta(s)*(1 + 1/2^s + 2/4^s)*(1 + 2/3^s). - _R. J. Mathar_, Apr 08 2011
%t A109015 GCD[Range[0,100],12] (* or *) PadRight[{},120,{12,1,2,3,4,1,6,1,4,3,2,1}] (* _Harvey P. Dale_, Dec 20 2018 *)
%o A109015 (Python)
%o A109015 from math import gcd
%o A109015 def a(n): return gcd(n, 12)
%o A109015 print([a(n) for n in range(99)]) # _Michael S. Branicky_, Dec 01 2021
%Y A109015 Cf. A109004.
%K A109015 nonn,easy,mult
%O A109015 0,1
%A A109015 _Mitch Harris_