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 A019845 #46 Aug 31 2025 10:03:12 %S A019845 5,8,7,7,8,5,2,5,2,2,9,2,4,7,3,1,2,9,1,6,8,7,0,5,9,5,4,6,3,9,0,7,2,7, %T A019845 6,8,5,9,7,6,5,2,4,3,7,6,4,3,1,4,5,9,9,1,0,7,2,2,7,2,4,8,0,7,5,7,2,7, %U A019845 8,4,7,4,1,6,2,3,5,1,9,5,7,5,0,8,5,0,4,0,4,9,8,6,2,7,4,1,3,3,5 %N A019845 Decimal expansion of sine of 36 degrees. %C A019845 This sequence is also decimal expansion of cosine of 54 degrees. - _Mohammad K. Azarian_, Jun 29 2013 %C A019845 The ratio of side to longer diagonal for any golden rhombus (see A019881). - _Rick L. Shepherd_, Apr 10 2017 %C A019845 Perimeter length of a regular pentagon with circumscribed unit circle. - _R. J. Mathar_, Aug 24 2023 %H A019845 Zak Seidov, <a href="/A019845/b019845.txt">Table of n, a(n) for n = 0..999</a> %H A019845 Wikipedia, <a href="http://en.wikipedia.org/wiki/Exact_trigonometric_constants">Exact trigonometric constants</a> %H A019845 <a href="/index/Al#algebraic_04">Index entries for algebraic numbers, degree 4</a> %F A019845 sin 36 degrees = sin Pi/5 radians = sqrt((1/8)(5 - sqrt(5))) = sqrt(A187798/2). %F A019845 Equals A019881/A001622. - _Rick L. Shepherd_, Apr 10 2017 %F A019845 This constant is (1/2)*A182007. - _Wolfdieter Lang_, May 08 2018 %F A019845 Equals 2*A019827*A019881. - _R. J. Mathar_, Jan 17 2021 %F A019845 Equals 5*A182007. - _R. J. Mathar_, Aug 24 2023 %F A019845 Equals cos(3*Pi/10). - _R. J. Mathar_, Aug 29 2025 %F A019845 Root of 16*x^4-20*x^2+5=0. Other 2 roots are +- A019881. - _R. J. Mathar_, Aug 29 2025 %F A019845 This^2+A019863^2=1. - _R. J. Mathar_, Aug 31 2025 %e A019845 sin 36 degrees = 0.587785252292473129168705954639... %t A019845 RealDigits[Sin[Pi/5], 10, 100][[1]] (* _Alonso del Arte_, Sep 19 2017 *) %t A019845 RealDigits[Sin[36 Degree],10,120][[1]] (* _Harvey P. Dale_, Aug 14 2018 *) %o A019845 (PARI) sin(Pi/5) \\ _Michel Marcus_, Apr 25 2015 %o A019845 (PARI) cos(3*Pi/10) \\ _Rick L. Shepherd_, Apr 10 2017 %o A019845 (PARI) real(I^(3/5)) \\ _Rick L. Shepherd_, Apr 10 2017 %Y A019845 Cf. A019827 (sine of 18 degrees), A019881 (sine of 72 degrees), A001622 (golden ratio phi). A182007. %K A019845 nonn,cons,easy,changed %O A019845 0,1 %A A019845 _N. J. A. Sloane_