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 A384909 #9 Jun 12 2025 10:17:13 %S A384909 1,2,3,4,2,2,9,9,4,7,9,6,0,4,5,1,9,7,6,8,3,0,4,6,2,4,6,6,5,0,6,7,3,0, %T A384909 9,5,4,0,6,0,4,2,4,6,5,0,4,9,9,3,1,8,2,0,3,3,2,9,2,4,2,0,2,8,6,4,8,4, %U A384909 5,1,9,4,5,5,4,2,1,4,6,7,1,6,2,0,2,2,3,7,0,1 %N A384909 Decimal expansion of the volume of an elongated pentagonal orthobicupola with unit edge. %C A384909 The elongated pentagonal orthobicupola is Johnson solid J_38. %C A384909 Also the volume of an elongated pentagonal gyrobicupola (Johnson solid J_39) with unit edge. %H A384909 Paolo Xausa, <a href="/A384909/b384909.txt">Table of n, a(n) for n = 2..10000</a> %H A384909 Wikipedia, <a href="https://en.wikipedia.org/wiki/Elongated_pentagonal_gyrobicupola">Elongated pentagonal gyrobicupola</a>. %H A384909 Wikipedia, <a href="https://en.wikipedia.org/wiki/Elongated_pentagonal_orthobicupola">Elongated pentagonal orthobicupola</a>. %F A384909 Equals (10 + 8*sqrt(5) + 15*sqrt(5 + 2*sqrt(5)))/6 = (10 + 8*A002163 + 15*sqrt(5 + A010476))/6. %F A384909 Equals the largest root of 1296*x^4 - 8640*x^3 - 82440*x^2 - 109200*x + 76525. %e A384909 12.342299479604519768304624665067309540604246504993... %t A384909 First[RealDigits[(10 + 8*Sqrt[5] + 15*Sqrt[5 + Sqrt[20]])/6, 10, 100]] (* or *) %t A384909 First[RealDigits[PolyhedronData["J38", "Volume"], 10, 100]] %Y A384909 Cf. A384625 (surface area - 10). %Y A384909 Cf. A002163, A010476, A384283, A384624, A384871. %K A384909 nonn,cons,easy %O A384909 2,2 %A A384909 _Paolo Xausa_, Jun 12 2025