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 A254676 #8 Oct 12 2024 17:08:37
%S A254676 1,235,2839,902101,10906669,3465871039,41903418691,13315875628969,
%T A254676 160992923703385,51159590700627091,618534770964985711,
%U A254676 196555134155933653885,2376410429054551397509,755164774267506397598311,9130168249892815504243099,2901342866180625423639056209
%N A254676 Heptagonal numbers (A000566) which are also centered triangular numbers (A005448).
%H A254676 Colin Barker, <a href="/A254676/b254676.txt">Table of n, a(n) for n = 1..558</a>
%H A254676 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,3842,-3842,-1,1).
%F A254676 a(n) = a(n-1)+3842*a(n-2)-3842*a(n-3)-a(n-4)+a(n-5).
%F A254676 G.f.: -x*(x^4+234*x^3-1238*x^2+234*x+1) / ((x-1)*(x^2-62*x+1)*(x^2+62*x+1)).
%e A254676 235 is in the sequence because it is the 10th heptagonal number and the 13th centered triangular number.
%t A254676 LinearRecurrence[{1,3842,-3842,-1,1},{1,235,2839,902101,10906669},20] (* _Harvey P. Dale_, Oct 12 2024 *)
%o A254676 (PARI) Vec(-x*(x^4+234*x^3-1238*x^2+234*x+1)/((x-1)*(x^2-62*x+1)*(x^2+62*x+1)) + O(x^100))
%Y A254676 Cf. A000566, A005448, A254674, A254675.
%K A254676 nonn,easy
%O A254676 1,2
%A A254676 _Colin Barker_, Feb 05 2015