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 A019830 #22 Dec 27 2021 20:58:02 %S A019830 3,5,8,3,6,7,9,4,9,5,4,5,3,0,0,2,7,3,4,8,4,1,3,7,7,8,9,4,1,3,4,6,6,8, %T A019830 3,4,1,9,1,5,4,4,4,4,9,4,6,0,0,1,3,7,9,5,4,6,3,5,7,6,7,7,5,8,5,7,3,1, %U A019830 9,9,2,5,9,8,2,4,9,9,0,9,8,9,8,7,3,1,6,0,9,1,3,9,2,9,8,6,7,8,9 %N A019830 Decimal expansion of sine of 21 degrees. %H A019830 Ivan Panchenko, <a href="/A019830/b019830.txt">Table of n, a(n) for n = 0..1000</a> %H A019830 Wikipedia, <a href="https://en.wikipedia.org/wiki/Trigonometric_constants_expressed_in_real_radicals">Trigonometric constants expressed in real radicals</a> %F A019830 Equals A019823*A019892 + A019816*A019885 = A019827*A019896 + A019812*A019881. - _R. J. Mathar_, Jan 27 2021 %t A019830 RealDigits[Sin[21 Degree],10,120][[1]] (* _Harvey P. Dale_, Apr 06 2016 *) %o A019830 (PARI) sin(7*Pi/60) \\ _Charles R Greathouse IV_, Jan 30 2016 %Y A019830 Cf. A019812, A019816, A019823, A019827, A019881, A019892, A019885, A019896. %K A019830 nonn,cons %O A019830 0,1 %A A019830 _N. J. A. Sloane_