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 A384138 #10 May 22 2025 05:22:40 %S A384138 2,0,2,1,9,8,0,2,3,2,9,8,4,7,9,1,4,9,3,4,4,2,7,2,7,5,4,6,9,1,9,0,7,9, %T A384138 4,4,2,5,5,0,7,3,3,2,6,8,3,2,7,3,4,5,2,3,4,3,8,5,0,4,8,7,5,8,9,1,5,9, %U A384138 7,4,0,3,0,7,7,7,2,0,8,1,0,2,1,4,1,3,7,5,1,7 %N A384138 Decimal expansion of the volume of an elongated pentagonal pyramid with unit edge. %C A384138 The elongated pentagonal pyramid is Johnson solid J_9. %H A384138 Paolo Xausa, <a href="/A384138/b384138.txt">Table of n, a(n) for n = 1..10000</a> %H A384138 Wikipedia, <a href="https://en.wikipedia.org/wiki/Elongated_pentagonal_pyramid">Elongated pentagonal pyramid</a>. %F A384138 Equals (5 + sqrt(5) + 6*sqrt(25 + 10*sqrt(5)))/24 = (5 + A002163 + 6*sqrt(25 + 10*A002163))/24. %F A384138 Equals the largest root of 20736*x^4 - 17280*x^3 - 59760*x^2 + 15600*x + 9025. %e A384138 2.0219802329847914934427275469190794425507332683273... %t A384138 First[RealDigits[(5 + Sqrt[5] + 6*Sqrt[25 + 10*Sqrt[5]])/24, 10, 100]] (* or *) %t A384138 First[RealDigits[PolyhedronData["J9", "Volume"], 10, 100]] %Y A384138 Cf. A179553 (surface area - 5). %Y A384138 Cf. A002163, A383852, A384139, A384140. %K A384138 nonn,cons,easy %O A384138 1,1 %A A384138 _Paolo Xausa_, May 20 2025