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 A231290 #17 Aug 13 2025 22:17:45
%S A231290 1,12,19,24,36,48,72,84,96,108,144,168,192,216,228,252,288,324,336,
%T A231290 361,384,432,456,504,576,588,648,672,684,744,756,768,816,864,912,972,
%U A231290 1008,1092,1152,1176,1296,1344,1368,1488,1512,1536,1596,1632,1728,1764
%N A231290 Numbers k dividing u(k), where the Lucas sequence is defined u(i) = u(i-1) - 5*u(i-2) with initial conditions u(0)=0, u(1)=1.
%C A231290 Contains every nonnegative power of 19. All terms that are not a power of 19 are multiples of 12.
%H A231290 C. Smyth, <a href="http://cs.uwaterloo.ca/journals/JIS/VOL13/Smyth/smyth2.html">The terms in Lucas sequences divisible by their indices</a>, Journal of Integer Sequences, Vol.13 (2010), Article 10.2.4.
%t A231290 nn = 3000; s = LinearRecurrence[{1, -5}, {1, 1}, nn]; t = {}; Do[If[Mod[s[[n]], n] == 0, AppendTo[t, n]], {n, nn}]; t (* _T. D. Noe_, Nov 08 2013 *)
%Y A231290 Cf. A001029 (powers of 19 (subsequence)).
%K A231290 nonn
%O A231290 0,2
%A A231290 _Thomas M. Bridge_, Nov 06 2013