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 A145504 #11 Jun 02 2025 00:39:32
%S A145504 4,22,526,277726,77132286526,5949389624883225721726,
%T A145504 35395236908668169265765137996816180039862526,
%U A145504 1252822795820745419377249396736955608088527968701950139470082687906021780162741058825726
%N A145504 a(n+1)=a(n)^2+2*a(n)-2 and a(1)=4.
%C A145504 General formula for a(n+1)=a(n)^2+2*a(n)-2 and a(1)=k+1 is a(n)=Floor[((k + Sqrt[k^2 + 4])/2)^(2^((n+1) - 1))
%C A145504 The next term (a(9)) has 175 digits. - _Harvey P. Dale_, Nov 16 2013
%F A145504 From Peter Bala, Nov 12 2012: (Start)
%F A145504 a(n) = alpha^(2^(n-1)) + (1/alpha)^(2^(n-1)) - 1, where alpha := 1/2*(5 + sqrt(21)).
%F A145504 a(n) = A003487(n-1) - 1.
%F A145504 Recurrence: a(n) = 6*{product {k = 1..n-1} a(k)} - 2 with a(1) = 4.
%F A145504 Product {n = 1..inf} (1 + 1/a(n)) = 2/7*sqrt(21).
%F A145504 Product {n = 1..inf} (1 + 2/(a(n) + 1)) = sqrt(7/3).
%F A145504 (End)
%t A145504 NestList[#^2+2#-2&,4,7] (* _Harvey P. Dale_, Nov 16 2013 *)
%Y A145504 A145502-A145510. A003487.
%K A145504 nonn
%O A145504 1,1
%A A145504 _Artur Jasinski_, Oct 11 2008
%E A145504 One additional term (a(8)) from _Harvey P. Dale_, Nov 16 2013