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 A387190 #8 Aug 24 2025 06:23:30 %S A387190 2,1,2,4,3,7,0,6,8,5,6,9,1,9,4,1,8,7,0,7,3,9,8,5,4,4,2,1,7,2,9,0,1,9, %T A387190 9,6,2,1,3,3,6,0,8,5,2,2,3,8,8,2,6,9,2,3,3,8,2,5,7,4,1,8,9,9,8,7,0,7, %U A387190 6,3,3,7,2,6,3,1,7,8,5,8,9,6,3,2,0,7,2,5,9,7 %N A387190 Decimal expansion of the second smallest dihedral angle, in radians, in an elongated pentagonal cupola (Johnson solid J_20). %C A387190 This is the dihedral angle between adjacent square faces at the edge where the prism and cupola parts of the solid meet. %C A387190 Also the analogous dihedral angle in Johnson solids J_38-J_41. %C A387190 Also the dihedral angle between a square face and a decagonal face in Johnson solids J_76-J_83. %H A387190 Paolo Xausa, <a href="/A387190/b387190.txt">Table of n, a(n) for n = 1..10000</a> %H A387190 Wikipedia, <a href="https://en.wikipedia.org/wiki/Elongated_pentagonal_cupola">Elongated pentagonal cupola</a>. %F A387190 Equals arccos(-sqrt((5 - sqrt(5))/10)) = arccos(-sqrt((5 - A002163)/10)). %e A387190 2.124370685691941870739854421729019962133608522388... %t A387190 First[RealDigits[ArcCos[-Sqrt[(5 - Sqrt[5])/10]], 10, 100]] (* or *) %t A387190 First[RealDigits[RankedMin[Union[PolyhedronData["J20", "DihedralAngles"]], 2], 10, 100]] %Y A387190 Cf. other J_20 dihedral angles: A019669, A228824, A377995, A377996, A387147. %Y A387190 Cf. A384144 (J_20 volume), A179591 (J_20 surface area - 10). %Y A387190 Cf. A002163. %K A387190 nonn,cons,easy,new %O A387190 1,1 %A A387190 _Paolo Xausa_, Aug 22 2025