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 A384625 #13 Jun 12 2025 12:59:31 %S A384625 1,7,7,7,1,0,8,1,8,2,0,1,0,0,1,2,7,0,7,9,3,3,6,6,3,9,8,0,8,5,4,1,9,0, %T A384625 0,1,1,6,1,7,1,7,6,1,4,7,4,5,4,6,3,4,8,2,2,8,5,5,3,7,0,6,8,6,2,6,7,7, %U A384625 5,7,0,5,2,6,6,8,9,9,3,2,5,5,5,3,6,7,7,4,7,9 %N A384625 Decimal expansion of the surface area of a pentagonal orthobicupola with unit edge. %C A384625 The pentagonal orthobicupola is Johnson solid J_30. %C A384625 Also the surface area of a pentagonal gyrobicupola (Johnson solid J_31) with unit edge. %H A384625 Paolo Xausa, <a href="/A384625/b384625.txt">Table of n, a(n) for n = 2..10000</a> %H A384625 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentagonal_orthobicupola">Pentagonal orthobicupola</a>. %H A384625 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentagonal_gyrobicupola">Pentagonal gyrobicupola</a>. %F A384625 Equals 10 + sqrt(5*(10 + sqrt(5) + sqrt(75 + 30*sqrt(5)))/2) = 10 + sqrt(5*(10 + A002163 + sqrt(75 + 30*A002163))/2). %F A384625 Equals the largest root of x^8 - 80*x^7 + 2700*x^6 - 50000*x^5 + 552750*x^4 - 3710000*x^3 + 14628125*x^2 - 30562500*x + 25328125. %e A384625 17.771081820100127079336639808541900116171761474546... %t A384625 First[RealDigits[10 + Sqrt[5*(10 + Sqrt[5] + Sqrt[75 + 30*Sqrt[5]])/2], 10, 100]] (* or *) %t A384625 First[RealDigits[PolyhedronData["J30", "SurfaceArea"], 10, 100]] %Y A384625 Cf. A384624 (volume). %Y A384625 Cf. A002163, A384284, A384286, A384872. %K A384625 nonn,cons,easy %O A384625 2,2 %A A384625 _Paolo Xausa_, Jun 05 2025