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 A253460 #12 Mar 12 2024 13:01:04 %S A253460 1,16,112,3937,28321,999856,7193296,253959361,1827068737,64504677712, %T A253460 464068265776,16383934179361,117871512438241,4161454776879856, %U A253460 29938900091047312,1056993129393303937,7604362751613578881,268472093411122320016,1931478200009757988336 %N A253460 Indices of centered heptagonal numbers (A069099) which are also centered square numbers (A001844). %C A253460 Also positive integers y in the solutions to 4*x^2 - 7*y^2 - 4*x + 7*y = 0, the corresponding values of x being A253459. %H A253460 Colin Barker, <a href="/A253460/b253460.txt">Table of n, a(n) for n = 1..832</a> %H A253460 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,254,-254,-1,1). %F A253460 a(n) = a(n-1)+254*a(n-2)-254*a(n-3)-a(n-4)+a(n-5). %F A253460 G.f.: -x*(x^4+15*x^3-158*x^2+15*x+1) / ((x-1)*(x^2-16*x+1)*(x^2+16*x+1)). %F A253460 a(n) = A105040(n) + 1. - _Michel Marcus_, Mar 12 2024 %e A253460 16 is in the sequence because the 16th centered heptagonal number is 841, which is also the 21st centered square number. %o A253460 (PARI) Vec(-x*(x^4+15*x^3-158*x^2+15*x+1)/((x-1)*(x^2-16*x+1)*(x^2+16*x+1)) + O(x^100)) %Y A253460 Cf. A001844, A069099, A253459, A253599. %K A253460 nonn,easy %O A253460 1,2 %A A253460 _Colin Barker_, Jan 01 2015