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 A230215 #18 Mar 25 2021 04:56:26
%S A230215 3,6,9,12,13,15,18,21,24,26,27,30,33,36,39,42,45,48,51,52,54,57,60,63,
%T A230215 65,66,69,72,75,78,81,84,87,90,91,93,96,99,102,104,105,108,111,114,
%U A230215 117,120,123,126,129,130,132,135,138,141,143,144,147,150,153,156
%N A230215 Numbers divisible by 3 or 13.
%C A230215 In general, sequences of numbers divisible by primes p and q will have the form a(n+p+q-1) = a(n) + p*q.
%C A230215 Union of A008585 and A008595 (0 excluded). - _Michel Marcus_, Oct 16 2013
%C A230215 The asymptotic density of this sequence is 5/13. - _Amiram Eldar_, Mar 25 2021
%H A230215 Amiram Eldar, <a href="/A230215/b230215.txt">Table of n, a(n) for n = 1..10000</a>
%H A230215 <a href="/index/Rec#order_16">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,-1).
%F A230215 a(n+15) = a(n) + 39.
%p A230215 for n from 1 to 138 do if n mod 3 = 0 or n mod 13= 0 then print(n) fi od
%t A230215 Select[Range[200], GCD[#, 39] > 1 &] (* _T. D. Noe_, Oct 15 2013 *)
%t A230215 With[{nn=60},Join[3*Range[nn],13*Floor[3/13 Range[nn]]]]//Union//Rest (* _Harvey P. Dale_, May 25 2020 *)
%o A230215 (PARI) is(n)=gcd(n,39)>1 \\ _Charles R Greathouse IV_, Dec 11 2013
%Y A230215 Complement of A229973.
%Y A230215 Cf. A008585, A008595.
%K A230215 nonn,easy
%O A230215 1,1
%A A230215 _Gary Detlefs_, Oct 11 2013