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 A104955 #18 Feb 16 2025 08:32:57 %S A104955 2,3,7,7,6,4,1,2,9,0,7,3,7,8,8,3,9,3,0,2,9,1,0,9,8,3,3,3,4,4,8,4,5,5, %T A104955 3,5,8,5,1,4,2,4,6,5,8,5,3,1,4,3,7,5,5,5,6,1,1,8,2,6,4,1,1,1,0,7,5,3, %U A104955 8,2,9,2,5,2,1,2,9,8,3,7,5,4,2,9,6,9,8,2,0,2,7,4,2,7,0,2,8,4,5,4,1,8,9,7,4 %N A104955 Decimal expansion of the area of the regular 5-gon (pentagon) of circumradius = 1. %C A104955 Equivalently, the area in the complex plane of the smallest convex set containing all order-5 roots of unity. %H A104955 Chai Wah Wu, <a href="/A104955/b104955.txt">Table of n, a(n) for n = 1..10001</a> %H A104955 Eric Weisstein et al., <a href="https://mathworld.wolfram.com/RootofUnity.html">Root of Unity</a>. %H A104955 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/deMoivreNumber.html">de Moivre Number</a>. %H A104955 <a href="/index/Al#algebraic_04">Index entries for algebraic numbers, degree 4</a>. %F A104955 Equals (5*sqrt((5 + sqrt(5))/2))/4. %e A104955 2.377641290737883930291098333448455358514246585314375556118264111075382925212... %t A104955 Floor[n/2]*Sin[(2*Pi)/n] - Sin[(4*Pi*Floor[n/2])/n]/2 /. n -> 5 %t A104955 RealDigits[(5(Sqrt[(5+Sqrt[5])/2]))/4,10,120][[1]] (* _Harvey P. Dale_, Jul 21 2013 *) %o A104955 (PARI) (5*sqrt((5 + sqrt(5))/2))/4 \\ _Michel Marcus_, Feb 24 2023 %Y A104955 Cf. A104954, A104956, A104957. %K A104955 nonn,cons %O A104955 1,1 %A A104955 Joseph Biberstine (jrbibers(AT)indiana.edu), Mar 30 2005