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 A387191 #10 Aug 25 2025 04:37:10 %S A387191 2,6,7,7,9,4,5,0,4,4,5,8,8,9,8,7,1,2,2,2,4,8,3,8,7,1,5,1,8,1,8,2,8,8, %T A387191 4,8,2,1,6,8,6,3,2,3,4,5,0,8,8,9,8,5,5,5,7,1,6,4,0,1,1,5,0,3,5,8,7,6, %U A387191 1,8,5,4,2,1,2,0,4,6,7,2,9,3,3,2,7,4,3,4,5,4 %N A387191 Decimal expansion of the second largest dihedral angle, in radians, in an elongated pentagonal rotunda (Johnson solid J_21). %C A387191 This is the dihedral angle between a square face and a pentagonal face. %C A387191 Also one of the dihedral angles in Johnson solids J_40-J_43, J_72-J_75, J_77-J_79 and J_82. %H A387191 Paolo Xausa, <a href="/A387191/b387191.txt">Table of n, a(n) for n = 1..10000</a> %H A387191 Wikipedia, <a href="https://en.wikipedia.org/wiki/Elongated_pentagonal_rotunda">Elongated pentagonal rotunda</a>. %F A387191 Equals Pi/2 + arctan(2) = A019669 + A105199. %F A387191 Equals arccos(-2*sqrt(5)/5) = arccos(-A010476/5). %e A387191 2.677945044588987122248387151818288482168632345... %t A387191 First[RealDigits[Pi/2 + ArcTan[2], 10, 100]] (* or *) %t A387191 First[RealDigits[RankedMax[Union[PolyhedronData["J21", "DihedralAngles"]], 2], 10, 100]] %Y A387191 Cf. other J_21 dihedral angles: A019669, A228824, A344075, A386530. %Y A387191 Cf. A384213 (J_21 volume), A179637 (J_21 surface area - 10). %Y A387191 Cf. A010476, A105199. %K A387191 nonn,cons,easy,new %O A387191 1,1 %A A387191 _Paolo Xausa_, Aug 22 2025