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 A275967 #9 Aug 27 2016 05:43:10 %S A275967 9,2,5,8,3,7,0,5,7,6,1,3,8,8,6,0,0,8,3,7,6,8,9,1,2,1,2,3,3,5,4,1,1,0, %T A275967 9,6,8,9,2,7,8,2,9,6,1,1,6,8,3,0,0,9,2,2,1,9,6,0,1,6,8,1,5,8,4,2,3,4, %U A275967 9,0,9,3,1,9,5,3,2,2,9,7,9,2,1,5,1,9,2,7,2,3,5,3,1,8,4,6,6,8,9,5,7,4 %N A275967 Decimal expansion of the area cut out by a rotating regular pentagon of width 1 inside a unit square. %C A275967 The part of the square not cut out is made of four congruent regions, one at each corner. Superficially they look like isosceles right triangles, but their "hypotenuses" curve very slightly outward. The region cut out by the pentagon is therefore concave. %H A275967 Jeremy Tan, <a href="https://math.stackexchange.com/questions/1886807/regular-pentagon-in-a-square/1892221#1892221">Regular pentagon in a square</a> (with derivation of constant) %F A275967 A = 1-(sqrt(5)-2)*Pi/10 = 0.92583705761388600837689121233541... %t A275967 First@ RealDigits@ N[1 - (Sqrt@ 5 - 2)/10 Pi, 120] (* _Michael De Vlieger_, Aug 15 2016 *) %o A275967 (PARI) 1-(sqrt(5)-2)*Pi/10 %Y A275967 Cf. A066666 (rotating Reuleaux triangle in a square). %K A275967 nonn,cons %O A275967 0,1 %A A275967 _Jeremy Tan_, Aug 14 2016