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 A254895 #6 Jun 13 2015 00:55:25 %S A254895 1,13,53,1241,5161,121573,505693,11912881,49552721,1167340733, %T A254895 4855660933,114387478921,475805218681,11208805593493,46624055769773, %U A254895 1098348560683361,4568681660219041,107626950141375853,447684178645696213,10546342765294150201 %N A254895 Indices of octagonal numbers (A000567) that are also centered square numbers (A001844). %C A254895 Also positive integers x in the solutions to 6*x^2 - 4*y^2 - 4*x + 4*y - 2 = 0, the corresponding values of y being A253673. %H A254895 Colin Barker, <a href="/A254895/b254895.txt">Table of n, a(n) for n = 1..1000</a> %H A254895 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,98,-98,-1,1). %F A254895 a(n) = a(n-1)+98*a(n-2)-98*a(n-3)-a(n-4)+a(n-5). %F A254895 G.f.: -x*(x^4+12*x^3-58*x^2+12*x+1) / ((x-1)*(x^2-10*x+1)*(x^2+10*x+1)). %e A254895 13 is in the sequence because the 13th octagonal number is 481, which is also the 16th centered square number. %o A254895 (PARI) Vec(-x*(x^4+12*x^3-58*x^2+12*x+1)/((x-1)*(x^2-10*x+1)*(x^2+10*x+1)) + O(x^100)) %Y A254895 Cf. A000567, A001844, A253673, A254896. %K A254895 nonn,easy %O A254895 1,2 %A A254895 _Colin Barker_, Feb 10 2015