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 A152119 #23 May 17 2025 13:26:22
%S A152119 1,1,1,6,7,41,48,281,329,1926,2255,13201,15456,90481,105937,620166,
%T A152119 726103,4250681,4976784,29134601,34111385,199691526,233802911,
%U A152119 1368706081,1602508992,9381251041,10983760033,64300051206,75283811239
%N A152119 a(n) = Product_{k=1..(n-1)/2} (5 + 4*cos(k*Pi/n)^2).
%H A152119 Paul Barry, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL12/Barry4/barry64.html">Symmetric Third-Order Recurring Sequences, Chebyshev Polynomials, and Riordan Arrays</a>, JIS 12 (2009) 09.8.6.
%H A152119 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,7,0,-1).
%F A152119 a(n) = Product_{k=1..(n-1)/2} (5 + 4*cos(k*Pi/n)^2).
%F A152119 From _Joerg Arndt_, Jan 24 2013: (Start)
%F A152119 a(n) = 7*a(n-2) - a(n-4).
%F A152119 G.f.: (x^4 - x^3 - 6*x^2 + x + 1)/((x^2 - 3*x + 1)*(x^2 + 3*x + 1)). (End)
%t A152119 a = Table[Product[5 + 4*Cos[k*Pi/n]^2, {k, 1, (n - 1)/2}], {n, 0, 10}]; FullSimplify[ExpandAll[a]]
%t A152119 Denominator[NestList[(5/(5+#))&,0,60]] (* _Vladimir Joseph Stephan Orlovsky_, Apr 13 2010 *)
%t A152119 LinearRecurrence[{0,7,0,-1},{1,1,1,6,7},30] (* _Harvey P. Dale_, May 17 2025 *)
%Y A152119 Cf. A004187 (bisection), A049685 (bisection).
%K A152119 nonn,easy
%O A152119 0,4
%A A152119 _Roger L. Bagula_ and _Gary W. Adamson_, Nov 24 2008