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 A254782 #16 Mar 01 2022 12:41:34
%S A254782 1,11,231,5061,111101,2439151,53550211,1175665481,25811090361,
%T A254782 566668322451,12440892003551,273132955755661,5996484134620981,
%U A254782 131649518005905911,2890292911995309051,63454794545890893201,1393115187097604341361,30585079321601404616731
%N A254782 Indices of centered hexagonal numbers (A003215) which are also centered pentagonal numbers (A005891).
%C A254782 Also positive integers y in the solutions to 5*x^2 - 6*y^2 - 5*x + 6*y = 0, the corresponding values of x being A133285.
%C A254782 The numbers (as opposed to the indices) are A133141.
%H A254782 Colin Barker, <a href="/A254782/b254782.txt">Table of n, a(n) for n = 1..746</a>
%H A254782 Giovanni Lucca, <a href="http://forumgeom.fau.edu/FG2016volume16/FG2016volume16.pdf#page=423">Circle Chains Inscribed in Symmetrical Lenses and Integer Sequences</a>, Forum Geometricorum, Volume 16 (2016) 419-427.
%H A254782 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (23,-23,1).
%F A254782 a(n) = 23*a(n-1)-23*a(n-2)+a(n-3).
%F A254782 G.f.: -x*(x^2-12*x+1) / ((x-1)*(x^2-22*x+1)).
%F A254782 a(n) = 1/2+1/24*(11+2*sqrt(30))^(-n)*(6+sqrt(30)-(-6+sqrt(30))*(11+2*sqrt(30))^(2*n)). - _Colin Barker_, Mar 03 2016
%e A254782 11 is in the sequence because the 11th centered hexagonal number is 331, which is also the 12th centered pentagonal number.
%t A254782 LinearRecurrence[{23,-23,1},{1,11,231},20] (* _Harvey P. Dale_, Mar 01 2022 *)
%o A254782 (PARI) Vec(-x*(x^2-12*x+1)/((x-1)*(x^2-22*x+1)) + O(x^100))
%Y A254782 Cf. A003215, A005891, A133141, A133285.
%K A254782 nonn,easy
%O A254782 1,2
%A A254782 _Colin Barker_, Feb 07 2015