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 A048905 #30 May 17 2025 00:33:38
%S A048905 1,315,151669,73103983,35235967977,16983663460771,8186090552123485,
%T A048905 3945678662460058839,1901808929215196236753,916667958203062126055947,
%U A048905 441832054044946729562729541,212962133381706120587109582655,102647306457928305176257256110009
%N A048905 Indices of octagonal numbers which are also heptagonal.
%C A048905 As n increases, this sequence is approximately geometric with common ratio r = lim_{n->oo} a(n)/a(n-1) = (sqrt(5)+sqrt(6))^4 = 241+44*sqrt(30). - _Ant King_, Dec 30 2011
%H A048905 Vincenzo Librandi, <a href="/A048905/b048905.txt">Table of n, a(n) for n = 1..200</a>
%H A048905 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/OctagonalHeptagonalNumber.html">Octagonal Heptagonal Number</a>
%H A048905 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (483,-483,1).
%F A048905 G.f.: -x*(1-168*x+7*x^2) / ( (x-1)*(x^2-482*x+1) ). - _R. J. Mathar_, Dec 21 2011
%F A048905 From _Ant King_, Dec 30 2011: (Start)
%F A048905 a(n) = 482*a(n-1)-a(n-2)-160.
%F A048905 a(n) = 1/120*((2*sqrt(5)+5*sqrt(6))*(sqrt(5)+sqrt(6))^(4*n-3) + (2*sqrt(5)-5*sqrt(6))*(sqrt(5)-sqrt(6))^(4*n-3)+40).
%F A048905 a(n) = ceiling(1/120*(2*sqrt(5)+5*sqrt(6))*(sqrt(5)+sqrt(6))^(4*n-3)). (End)
%t A048905 LinearRecurrence[{483,-483,1},{1,315,151669},20] (* _Vincenzo Librandi_, Dec 28 2011 *)
%Y A048905 Cf. A048904, A048906.
%K A048905 nonn,easy
%O A048905 1,2
%A A048905 _Eric W. Weisstein_