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 A386852 #18 Aug 19 2025 10:38:12 %S A386852 6,5,2,3,5,8,1,3,9,7,8,4,3,6,8,1,8,5,9,9,5,3,9,0,6,3,1,6,4,3,8,2,2,5, %T A386852 7,4,3,6,5,3,0,7,9,1,9,9,6,2,9,7,9,7,4,1,7,9,4,7,2,7,9,4,6,7,0,6,1,4, %U A386852 3,5,8,3,8,2,1,0,3,9,5,3,2,9,0,9,5,6,7,1,4,4 %N A386852 Decimal expansion of the dihedral angle, in radians, between the pentagonal face and a triangular face in a pentagonal pyramid with equal edges (Johnson solid J_2). %C A386852 Also the dihedral angle, in radians, between the 10-gonal face and a triangular face in a pentagonal cupola (Johnson solid J_5) %H A386852 Paolo Xausa, <a href="/A386852/b386852.txt">Table of n, a(n) for n = 0..10000</a> %H A386852 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentagonal_cupola">Pentagonal cupola</a>. %H A386852 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentagonal_pyramid">Pentagonal pyramid</a>. %H A386852 <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a>. %F A386852 Equals arcsec(sqrt(15 - 6*sqrt(5))) = arcsec(sqrt(15 - 6*A002163)). %F A386852 Equals arccos(sqrt((5 + 2*sqrt(5))/15)) = arccos(sqrt((5 + A010476)/15)). %e A386852 0.65235813978436818599539063164382257436530791996... %t A386852 First[RealDigits[ArcSec[Sqrt[15 - 6*Sqrt[5]]], 10, 100]] (* or *) %t A386852 First[RealDigits[Min[PolyhedronData["J2", "DihedralAngles"]], 10, 100]] %o A386852 (PARI) acos(sqrt((5+2*sqrt(5))/15)) \\ _Charles R Greathouse IV_, Aug 19 2025 %Y A386852 Cf. A179552 (J_2 volume), A179553 (J_2 surface area). %Y A386852 Cf. A179590 (J_5 volume), A179591 (J_5 surface area). %Y A386852 Cf. A002163, A010476. %K A386852 nonn,cons,easy %O A386852 0,1 %A A386852 _Paolo Xausa_, Aug 05 2025