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 A380004 #7 Jan 13 2025 04:14:29 %S A380004 2,0,6,1,8,7,3,0,3,4,3,2,4,4,0,7,3,5,5,8,6,6,0,9,8,1,7,6,0,8,9,3,1,5, %T A380004 9,9,2,9,2,1,0,5,0,6,9,0,8,8,1,7,9,8,1,4,7,1,5,3,9,7,5,0,9,8,5,0,0,0, %U A380004 3,1,5,5,5,3,0,6,9,1,6,7,9,7,3,5,7,8,9,3,7,1 %N A380004 Decimal expansion of obtuse vertex angles, in radians, in a pentagonal hexecontahedron face. %C A380004 A pentagonal hexecontahedron face is an irregular pentagon with one acute angle (A380003) and four (equal) obtuse angles (this constant). %H A380004 Paolo Xausa, <a href="/A380004/b380004.txt">Table of n, a(n) for n = 1..10000</a> %H A380004 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PentagonalHexecontahedron.html">Pentagonal Hexecontahedron</a>. %H A380004 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentagonal_hexecontahedron">Pentagonal hexecontahedron</a>. %F A380004 Equals arccos(c), where c is the smallest real root of 64*x^6 - 128*x^5 + 64*x^4 + 24*x^3 - 24*x^2 + 1. %F A380004 Equals (3*Pi - A380003)/4. %e A380004 2.06187303432440735586609817608931599292105069088... %t A380004 First[RealDigits[ArcCos[Root[64*#^6 - 128*#^5 + 64*#^4 + 24*#^3 - 24*#^2 + 1 &, 1]], 10, 100]] %Y A380004 Cf. A379888 (surface area), A379889 (volume), A379890 (inradius), A379890 (midradius), A379892 (dihedral angle), A380002 (long/short edge length ratio), A380003 (face acute angle). %K A380004 nonn,cons,easy %O A380004 1,1 %A A380004 _Paolo Xausa_, Jan 12 2025