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 A384952 #7 Jun 20 2025 14:22:41 %S A384952 2,1,5,2,9,7,3,4,7,7,9,1,8,7,5,3,7,6,4,6,2,5,1,7,1,8,5,0,1,4,9,7,5,5, %T A384952 7,2,2,7,0,9,8,5,0,7,3,7,7,7,4,3,8,0,3,9,5,3,0,3,2,0,9,9,4,8,7,9,3,3, %U A384952 6,3,4,1,7,7,2,1,1,5,0,7,8,4,4,4,7,7,3,2,5,1 %N A384952 Decimal expansion of the volume of an elongated pentagonal orthobirotunda with unit edge. %C A384952 The elongated pentagonal orthobirotunda is Johnson solid J_42. %C A384952 Also the volume of an elongated pentagonal gyrobirotunda (Johnson solid J_43) with unit edge. %H A384952 Paolo Xausa, <a href="/A384952/b384952.txt">Table of n, a(n) for n = 2..10000</a> %H A384952 Wikipedia, <a href="https://en.wikipedia.org/wiki/Elongated_pentagonal_gyrobirotunda">Elongated pentagonal gyrobirotunda</a>. %H A384952 Wikipedia, <a href="https://en.wikipedia.org/wiki/Elongated_pentagonal_orthobirotunda">Elongated pentagonal orthobirotunda</a>. %F A384952 Equals (45 + 17*sqrt(5) + 15*sqrt(5 + 2*sqrt(5)))/6 = (45 + 17*A002163 + 15*sqrt(5 + A010476))/6. %F A384952 Equals the largest root of 1296*x^4 - 38880*x^3 + 252360*x^2 - 329400*x - 332975. %e A384952 21.52973477918753764625171850149755722709850737774... %t A384952 First[RealDigits[(45 + 17*Sqrt[5] + 15*Sqrt[5 + Sqrt[20]])/6, 10, 100]] (* or *) %t A384952 First[RealDigits[PolyhedronData["J42", "Volume"], 10, 100]] %Y A384952 Cf. A179451 (surface area - 10), A344149 (surface area + 20). %Y A384952 Cf. A002163, A010476, A384283, A384285, A384624, A384871, A384909, A384910. %K A384952 nonn,cons,easy %O A384952 2,1 %A A384952 _Paolo Xausa_, Jun 20 2025