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 A019815 #30 Aug 31 2025 11:43:23 %S A019815 1,0,4,5,2,8,4,6,3,2,6,7,6,5,3,4,7,1,3,9,9,8,3,4,1,5,4,8,0,2,4,9,8,1, %T A019815 1,9,0,8,0,6,5,5,8,6,9,4,7,4,5,9,3,1,1,3,9,9,3,2,7,5,4,7,6,7,1,2,4,8, %U A019815 4,6,5,0,6,9,3,1,8,0,0,4,6,8,2,8,1,8,0,3,9,8,7,9,8,6,0,4,4,2,6 %N A019815 Decimal expansion of sine of 6 degrees. %C A019815 Decimal expansion of 1/8 (-1 - sqrt(5) + sqrt(6*(5 - sqrt(5)))). - _Artur Jasinski_, Oct 28 2008 %H A019815 Ivan Panchenko, <a href="/A019815/b019815.txt">Table of n, a(n) for n = 0..1000</a> %H A019815 Wikipedia, <a href="http://en.wikipedia.org/wiki/Exact_trigonometric_constants">Exact trigonometric constants</a> %H A019815 <a href="/index/Al#algebraic_04">Index entries for algebraic numbers, degree 4</a> %F A019815 Equals cos(7*Pi/15) = -cos(8*Pi/15) = 2F1(6/5,-1/5;1/2;3/4) / 2 = -2F1(13/10,-3/10;1/2;3/4) / 2. - _R. J. Mathar_, Oct 27 2008 %F A019815 Equals 2*A019812*A019896. - _R. J. Mathar_, Jan 17 2021 %F A019815 Smallest positive of the 4 real-valued roots of 16*x^4+8*x^3-16*x^2-8*x+1=0. (Other A019887, -A019875, -A019851) - _R. J. Mathar_, Aug 31 2025 %e A019815 sin(Pi/30) = 0.10452846... %t A019815 First[RealDigits[1/8 (-1 - Sqrt[5] + Sqrt[6 (5 - Sqrt[5])]), 10, 100]] (* _Artur Jasinski_, Oct 28 2008 *) %t A019815 RealDigits[Sin[6 Degree],10,120][[1]] (* _Harvey P. Dale_, Apr 27 2012 *) %o A019815 (PARI) sin(Pi/30) \\ _Charles R Greathouse IV_, Jan 30 2016 %K A019815 nonn,cons,changed %O A019815 0,3 %A A019815 _N. J. A. Sloane_