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 A254709 #8 Aug 08 2017 16:15:12
%S A254709 1,2,10,25,137,346,1906,4817,26545,67090,369722,934441,5149561,
%T A254709 13015082,71724130,181276705,998988257,2524858786,13914111466,
%U A254709 35166746297,193798572265,489809589370,2699265900242,6822167504881,37595924031121,95020535478962
%N A254709 Indices of pentagonal numbers (A000326) which are also centered square numbers (A001844).
%C A254709 Also positive integers x in the solutions to 3*x^2 - 4*y^2 - x + 4*y - 2 = 0, the corresponding values of y being A254710.
%H A254709 Colin Barker, <a href="/A254709/b254709.txt">Table of n, a(n) for n = 1..1000</a>
%H A254709 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,14,-14,-1,1).
%F A254709 a(n) = a(n-1)+14*a(n-2)-14*a(n-3)-a(n-4)+a(n-5).
%F A254709 G.f.: -x*(x^4+x^3-6*x^2+x+1) / ((x-1)*(x^2-4*x+1)*(x^2+4*x+1)).
%e A254709 10 is in the sequence because the 10th pentagonal number is 145, which is also the 9th centered square number.
%t A254709 LinearRecurrence[{1,14,-14,-1,1},{1,2,10,25,137},30] (* _Harvey P. Dale_, Aug 08 2017 *)
%o A254709 (PARI) Vec(-x*(x^4+x^3-6*x^2+x+1)/((x-1)*(x^2-4*x+1)*(x^2+4*x+1)) + O(x^100))
%Y A254709 Cf. A000326, A001844, A254710, A254711.
%K A254709 nonn,easy
%O A254709 1,2
%A A254709 _Colin Barker_, Feb 06 2015