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 A253714 #7 Jun 13 2015 00:55:21 %S A253714 1,2857,45529,184300369,2937241777,11889953986681,189493215939721, %T A253714 767068491312421537,12224965330197902689,49486656636639609035209, %U A253714 788681413122894278122297,3192582165489099245985035761,50880992673985436128583949841 %N A253714 Indices of hexagonal numbers (A000384) which are also centered heptagonal numbers (A069099). %C A253714 Also positive integers x in the solutions to 4*x^2-7*y^2-2*x+7*y-2 = 0, the corresponding values of y being A253715. %H A253714 Colin Barker, <a href="/A253714/b253714.txt">Table of n, a(n) for n = 1..416</a> %H A253714 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,64514,-64514,-1,1). %F A253714 a(n) = a(n-1)+64514*a(n-2)-64514*a(n-3)-a(n-4)+a(n-5). %F A253714 G.f.: -x*(x^4+2856*x^3-21842*x^2+2856*x+1) / ((x-1)*(x^2-254*x+1)*(x^2+254*x+1)). %e A253714 2857 is in the sequence because the 2857th hexagonal number is 16322041, which is also the 2160th centered heptagonal number. %o A253714 (PARI) Vec(-x*(x^4+2856*x^3-21842*x^2+2856*x+1)/((x-1)*(x^2-254*x+1)*(x^2+254*x+1)) + O(x^100)) %Y A253714 Cf. A000384, A069099, A253715, A253716. %K A253714 nonn,easy %O A253714 1,2 %A A253714 _Colin Barker_, Jan 10 2015