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 A373017 #8 Jul 16 2024 12:01:24
%S A373017 5,5,0,7,4,0,2,9,0,8,6,6,9,4,0,5,7,1,8,6,1,0,6,8,3,7,8,9,8,2,3,0,7,8,
%T A373017 3,3,0,1,3,5,3,3,4,2,6,7,8,3,5,9,2,1,1,9,5,7,4,0,9,1,1,9,5,6,7,5,5,5,
%U A373017 1,9,1,3,0,8,9,4,0,7,9,4,5,9,8,1,9,0
%N A373017 Decimal expansion of Sum_{k>=0} (sin(k*Pi/5))^2/2^k.
%C A373017 Minimal polynomial is 124x^2 - 150x + 45. - _Charles R Greathouse IV_, Jul 16 2024
%H A373017 <a href="/index/Al#algebraic_02">Index entries for algebraic numbers, degree 2</a>
%F A373017 Equals (3/124) (25 - sqrt(5)).
%e A373017 0.5507402908669405718610683789823078330135334267835...
%t A373017 s = Sum[(Sin[k Pi/5])^2/2^k, {k, 0, Infinity}]
%t A373017 d = N[s, 100]
%t A373017 First[RealDigits[d]]
%o A373017 (PARI) suminf(k=0,(sin(k*Pi/5))^2>>k) \\ _Charles R Greathouse IV_, Jul 16 2024
%o A373017 (PARI) (75-sqrt(45))/124 \\ _Charles R Greathouse IV_, Jul 16 2024
%Y A373017 Cf. A373021.
%K A373017 nonn,cons
%O A373017 0,1
%A A373017 _Clark Kimberling_, Jul 16 2024