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 A367480 #86 Aug 29 2025 15:23:40 %S A367480 1,3,0,4,7,6,4,8,7,0,9,6,2,4,8,6,5,0,5,2,4,1,1,5,0,2,2,3,5,4,6,8,5,5, %T A367480 1,1,3,4,4,4,5,0,1,8,8,7,6,0,6,3,2,1,1,6,2,0,6,3,1,0,6,2,9,6,4,6,6,8, %U A367480 5,3,3,4,2,7,7,8,4,7,9,5,9,6,3,7,9,1,1,1,4,2,1,9,7,4,7,6,1,7,9,3,6,1,5,1,5 %N A367480 Decimal expansion of the radius of a common circle surrounded by seven tangent unit circles. %C A367480 The radius of a common circle surrounded by n tangent unit circles (n > 2) is r = 1/sin(Pi/n) - 1. %C A367480 n=7 is the smallest number for which the radius cannot be expressed using square roots, since the regular heptagon formed by the centers of the tangent circles is non-constructible (see A246724, A188582, and A121570 for n=3, 4, 5). %H A367480 Andrew M. Gleason, <a href="https://doi.org/10.2307/2323624">Angle Trisection, the Heptagon, and the Triskaidecagon</a>, The American Mathematical Monthly 95, no. 3 (March 1988), pp. 185-194. %H A367480 <a href="/index/Al#algebraic_06">Index entries for algebraic numbers, degree 6</a>. %F A367480 Equals 1 / sin(Pi/7) - 1. %F A367480 Equals A121598 - 1. %F A367480 Largest of the 6 real-valued roots of 7*x^6+ 42*x^5 +49*x^4 -84*x^3 -119*x^2 +42*x-1=0. - _R. J. Mathar_, Aug 29 2025 %e A367480 1.3047648709624865052... %t A367480 RealDigits[Csc[Pi/7] - 1, 10, 120][[1]] (* _Amiram Eldar_, Dec 28 2023 *) %o A367480 (PARI) 1/sin(Pi/7) - 1 %Y A367480 Cf. A121598. %Y A367480 Cf. A121570, A188582, A246724. %K A367480 nonn,cons,easy,changed %O A367480 1,2 %A A367480 _Thomas Otten_, Dec 23 2023 %E A367480 More digits from _Jon E. Schoenfield_, Dec 24 2023 %E A367480 Comments edited by _Michal Paulovic_, Dec 26 2023