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 A298123 #15 Feb 16 2025 08:33:53
%S A298123 15,111,38801,2445586864035,1080118354441207408343642986146950633
%N A298123 Number of connected induced subgraphs in the n-Apollonian network.
%C A298123 Term a(6) has 108 decimal digits and a(7) has 323 decimal digits. - _Andrew Howroyd_, Jan 16 2018
%H A298123 Andrew Howroyd, <a href="/A298123/b298123.txt">Table of n, a(n) for n = 1..7</a>
%H A298123 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ApollonianNetwork.html">Apollonian Network</a>
%H A298123 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ConnectedGraph.html">Connected Graph</a>
%H A298123 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Vertex-InducedSubgraph.html">Vertex-Induced Subgraph</a>
%t A298123 {1, 3, 3, 1} . # & /@ NestList[Function[{t0, t1, t2, t3}, {3 t0 + t1^3, t1^2 + t1 t2^2, t1^2 t2 + t2^2 t3, t2^3 + t3^3}] @@ # &, {1, 2, 2, 2}, 4] (* _Eric W. Weisstein_, Jan 17 2018 *)
%o A298123 (PARI) \\ here t0..t3 are for 0..3 outside vertices included in set.
%o A298123 D(t0,t1,t2,t3)={[3*t0 + t1^3, t1^2 + t1*t2^2, t1^2*t2 + t2^2*t3, t2^3 + t3^3]}
%o A298123 a(n)={my(v=[1,2,2,2]); for(i=2, n, v=D(v[1], v[2], v[3], v[4])); v[1]+3*v[2]+3*v[3]+v[4]} \\ _Andrew Howroyd_, Jan 16 2018
%Y A298123 Cf. A298105.
%K A298123 nonn
%O A298123 1,1
%A A298123 _Eric W. Weisstein_, Jan 13 2018
%E A298123 Terms a(4) and beyond from _Andrew Howroyd_, Jan 16 2018