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 A019821 #32 Aug 31 2025 11:16:41 %S A019821 2,0,7,9,1,1,6,9,0,8,1,7,7,5,9,3,3,7,1,0,1,7,4,2,2,8,4,4,0,5,1,2,5,1, %T A019821 6,6,2,1,6,5,8,4,7,6,0,6,2,7,7,2,3,8,3,6,4,0,7,1,8,1,9,7,3,8,8,2,3,8, %U A019821 2,8,2,5,6,6,4,0,7,4,3,7,6,3,0,4,6,2,8,7,5,6,7,2,2,7,2,7,5,7,3 %N A019821 Decimal expansion of sine of 12 degrees. %C A019821 An algebraic number of degree 8 and denominator 2. - _Charles R Greathouse IV_, Aug 27 2017 %H A019821 Ivan Panchenko, <a href="/A019821/b019821.txt">Table of n, a(n) for n = 0..1000</a> %H A019821 Wikipedia, <a href="https://en.wikipedia.org/wiki/Exact_trigonometric_constants">Exact trigonometric constants</a> %H A019821 <a href="/index/Al#algebraic_08">Index entries for algebraic numbers, degree 8</a> %F A019821 Equals sin(Pi/15) = sqrt(1-A019887^2) = (sqrt(5)-1)*(sqrt(5+2*sqrt(5)) - sqrt(3))/8. - _R. J. Mathar_, Jun 18 2006 %F A019821 Equals 2*A019815*A019893. - _R. J. Mathar_, Jan 17 2021 %F A019821 Smallest positive of the 8 real-valued roots of 256*x^8-448*x^6+224*x^4-32*x^2+1 =0. (Other A019893, A019833, A019857)- _R. J. Mathar_, Aug 31 2025 %e A019821 0.20791169... %t A019821 RealDigits[N[Sin[Pi/15], 110]][[1]] (* _Wesley Ivan Hurt_, Dec 27 2021 *) %o A019821 (PARI) sin(Pi/15) \\ _Charles R Greathouse IV_, Aug 27 2017 %Y A019821 Cf. A019815, A019887, A019893. %K A019821 nonn,cons,changed %O A019821 0,1 %A A019821 _N. J. A. Sloane_