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 A387189 #12 Aug 21 2025 11:15:02 %S A387189 1,3,0,4,7,1,6,2,7,9,5,6,8,7,3,6,3,7,1,9,9,0,7,8,1,2,6,3,2,8,7,6,4,5, %T A387189 1,4,8,7,3,0,6,1,5,8,3,9,9,2,5,9,5,9,4,8,3,5,8,9,4,5,5,8,9,3,4,1,2,2, %U A387189 8,7,1,6,7,6,4,2,0,7,9,0,6,5,8,1,9,1,3,4,2,8 %N A387189 Decimal expansion of the smallest dihedral angle, in radians, in a pentagonal bipyramid (Johnson solid J_13). %C A387189 This is the dihedral angle between triangular faces at the edge where the two pyramidal parts of the solid meet. %C A387189 Also the dihedral angle between triangular faces in a pentagonal orthobicupola (Johnson solid J_30). %H A387189 Paolo Xausa, <a href="/A387189/b387189.txt">Table of n, a(n) for n = 1..10000</a> %H A387189 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentagonal_bipyramid">Pentagonal bipyramid</a>. %H A387189 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentagonal_orthobicupola">Pentagonal orthobicupola</a>. %F A387189 Equals arccos((4*sqrt(5) - 5)/15) = arccos((A010532 - 5)/15). %F A387189 Equals 2*A386852. %e A387189 1.3047162795687363719907812632876451487306158399... %t A387189 First[RealDigits[ArcCos[(Sqrt[80] - 5)/15], 10, 100]] (* or *) %t A387189 First[RealDigits[Min[PolyhedronData["J13", "DihedralAngles"]], 10, 100]] %Y A387189 Cf. A236367 (J_13 smallest dihedral angle). %Y A387189 Cf. other J_30 dihedral angles: A105199, A377995, A377996. %Y A387189 Cf. A179641 (J_13 volume), A120011 (J_13 surface area, divided by 10). %Y A387189 Cf. A384624 (J_30 volume), A384625 (J_30 surface area). %Y A387189 Cf. A010532, A386852. %K A387189 nonn,cons,easy %O A387189 1,2 %A A387189 _Paolo Xausa_, Aug 21 2025