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 A019818 #41 Sep 03 2025 03:46:50 %S A019818 1,5,6,4,3,4,4,6,5,0,4,0,2,3,0,8,6,9,0,1,0,1,0,5,3,1,9,4,6,7,1,6,6,8, %T A019818 9,2,3,1,3,8,9,9,8,9,2,0,8,5,6,6,0,7,9,0,0,8,4,6,4,1,3,4,6,0,5,7,7,5, %U A019818 8,7,9,3,3,0,5,6,2,3,5,7,9,3,3,6,6,9,5,8,7,2,6,7,6,8,4,8,6,8,8 %N A019818 Decimal expansion of sine of 9 degrees. %C A019818 Also the imaginary part of i^(1/10). - _Stanislav Sykora_, Apr 25 2012 %C A019818 An algebraic number of degree 8 and denominator 2. - _Charles R Greathouse IV_, Aug 27 2017 %H A019818 Ivan Panchenko, <a href="/A019818/b019818.txt">Table of n, a(n) for n = 0..1000</a> %H A019818 Wikipedia, <a href="https://en.wikipedia.org/wiki/Exact_trigonometric_constants">Exact trigonometric constants</a> %H A019818 <a href="/index/Al#algebraic_08">Index entries for algebraic numbers, degree 8</a> %F A019818 sqrt(8-2*sqrt(10+2*sqrt(5)))/4 = sqrt((1/2)*(1 - sqrt((1/8)*(5 + sqrt(5))))). - Herman Jamke (hermanjamke(AT)fastmail.fm), Nov 13 2006 %F A019818 Equals A019815*A019896 + A019812*A019893. - _R. J. Mathar_, Jan 27 2021 %F A019818 This^2 + A019890^2=1. - _R. J. Mathar_, Aug 31 2025 %F A019818 Smallest positive of the 8 real-valued roots of 256*x^8 -512*x^6 +304*x^4 -48*x^2+1=0. - _R. J. Mathar_, Aug 31 2025 %e A019818 sin(Pi/20) = 0.1564344650402308690101053194671668923138... %t A019818 RealDigits[Sin[9 Degree],10,120][[1]] (* _Harvey P. Dale_, Sep 15 2014 *) %o A019818 (PARI) sin(Pi/20) \\ _Charles R Greathouse IV_, Aug 27 2017 %Y A019818 Cf. A019812, A019815, A019893, A019896. %K A019818 nonn,cons,changed %O A019818 0,2 %A A019818 _N. J. A. Sloane_