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 A384285 #9 May 30 2025 10:34:51 %S A384285 1,3,6,6,7,0,5,0,8,4,3,6,7,1,6,9,6,9,3,2,1,2,3,5,3,0,8,9,9,2,3,3,2,8, %T A384285 6,5,6,5,4,0,0,2,6,4,3,6,6,9,7,8,9,8,4,4,5,2,0,1,7,4,8,2,0,5,9,2,2,8, %U A384285 3,2,4,2,3,2,9,5,6,5,7,3,8,8,1,5,9,0,1,0,0,2 %N A384285 Decimal expansion of the volume of a gyroelongated pentagonal rotunda with unit edge. %C A384285 The gyroelongated pentagonal rotunda is Johnson solid J_25. %H A384285 Paolo Xausa, <a href="/A384285/b384285.txt">Table of n, a(n) for n = 2..10000</a> %H A384285 Wikipedia, <a href="https://en.wikipedia.org/wiki/Gyroelongated_pentagonal_rotunda">Gyroelongated pentagonal rotunda</a>. %F A384285 Equals (45 + 17*sqrt(5) + 10*sqrt(2*(sqrt(650 + 290*sqrt(5)) - sqrt(5) - 1)))/12 = (45 + 17*A002163 + 10*sqrt(2*(sqrt(650 + 290*A002163) - A002163 - 1)))/12. %F A384285 Equals the largest real root of 1679616*x^8 - 50388480*x^7 + 603262080*x^6 - 3520972800*x^5 + 5215460400*x^4 + 4128624000*x^3 - 8894943000*x^2 + 3881385000*x - 424924375. %e A384285 13.667050843671696932123530899233286565400264... %t A384285 First[RealDigits[(45 + 17*# + 10*Sqrt[2*(Sqrt[650 + 290*#] - # - 1)])/12 & [Sqrt[5]], 10, 100]] (* or *) %t A384285 First[RealDigits[PolyhedronData["J25", "Volume"], 10, 100]] %Y A384285 Cf. A384286 (surface area). %Y A384285 Cf. A002163, A179590, A179639, A179641, A384138, A384140, A384144, A384213, A384283. %K A384285 nonn,cons,easy %O A384285 2,2 %A A384285 _Paolo Xausa_, May 29 2025