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 A280633 #16 Feb 11 2025 14:22:29 %S A280633 3,1,2,5,6,6,7,1,9,8,0,0,4,7,4,6,2,7,9,3,3,0,8,9,9,2,8,1,8,4,7,6,6,6, %T A280633 3,2,8,0,0,6,7,6,2,1,8,9,3,1,3,2,4,8,9,7,0,2,5,2,3,4,4,8,0,6,3,7,7,1, %U A280633 8,4,7,9,8,5,0,2,2,6,5,2,3,7,5,8,7,2,9,9,0,3,6,8,3,3,1,9,2,3,3,2,2,1,5,2,6 %N A280633 Decimal expansion of 18*sin(Pi/18). %C A280633 The ratio of the perimeter of a regular 9-gon (nonagon) to its diameter (largest diagonal). %C A280633 Also least positive root of x^3 - 243x + 729. %H A280633 <a href="/index/Al#algebraic_03">Index entries for algebraic numbers, degree 3</a>. %F A280633 18*A019819. %e A280633 3.125667198004746279330899281847666328006762189313248970252344806377184798... %p A280633 evalf(18*sin(Pi/18),100); # _Wesley Ivan Hurt_, Feb 01 2017 %t A280633 RealDigits[18*Sin[Pi/18],10,120][[1]] (* _Harvey P. Dale_, Dec 02 2018 *) %o A280633 (PARI) 18*sin(Pi/18) %Y A280633 Cf. For other n-gons: A010466 (n=4), 10*A019827 (n=5, 10), A280533 (n=7),A280585 (n=8), A280725(n=11), A280819 (n=12). %K A280633 nonn,cons %O A280633 1,1 %A A280633 _Rick L. Shepherd_, Jan 06 2017