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 A046179 #47 Feb 16 2025 08:32:39
%S A046179 1,143,27693,5372251,1042188953,202179284583,39221739020101,
%T A046179 7608815190614963,1476070925240282673,286350150681424223551,
%U A046179 55550453161271059086173,10776501563135904038493963,2090585752795204112408742601,405562859540706461903257570583
%N A046179 Indices of hexagonal numbers that are also pentagonal.
%C A046179 As n increases, this sequence is approximately geometric with common ratio r = lim_{n->infinity} a(n)/a(n-1) = (2+sqrt(3))^4 = 97 + 56*sqrt(3). - _Ant King_, Dec 14 2011
%H A046179 Colin Barker, <a href="/A046179/b046179.txt">Table of n, a(n) for n = 1..438</a>
%H A046179 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HexagonalPentagonalNumber.html">Hexagonal Pentagonal Number</a>.
%H A046179 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (195,-195,1).
%F A046179 From _Warut Roonguthai_, Jan 08 2001: (Start)
%F A046179 a(n) = 194*a(n-1) - a(n-2) - 48.
%F A046179 G.f.: x*(1-52*x+3*x^2)/((1-x)*(1-194*x+x^2)). (End)
%F A046179 From _Ant King_, Dec 14 2011: (Start)
%F A046179 a(n) = 195*a(n-1) - 195*a(n-2) + a(n-3).
%F A046179 a(n) = (1/24)*sqrt(3)*((sqrt(3)-1)*(2+sqrt(3))^(4n-2)+(sqrt(3)+1)* (2-sqrt(3))^(4n-2)+2*sqrt(3)).
%F A046179 a(n) = ceiling((1/24)*sqrt(3)*(sqrt(3)-1)*(2+sqrt(3))^(4n-2)).
%F A046179 (End)
%F A046179 a(n) = A276915(2n-1). - _Daniel Poveda Parrilla_, Dec 03 2016
%t A046179 LinearRecurrence[{195, -195, 1}, {1, 143, 27693}, 11] (* _Ant King_, Dec 14 2011 *)
%o A046179 (PARI) Vec(-x*(3*x^2-52*x+1)/((x-1)*(x^2-194*x+1)) + O(x^20)) \\ _Colin Barker_, Jun 21 2015
%Y A046179 Cf. A046178, A046180, A276915.
%K A046179 nonn,easy
%O A046179 1,2
%A A046179 _Eric W. Weisstein_