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 A019699 #46 Oct 19 2024 15:57:32 %S A019699 4,1,8,8,7,9,0,2,0,4,7,8,6,3,9,0,9,8,4,6,1,6,8,5,7,8,4,4,3,7,2,6,7,0, %T A019699 5,1,2,2,6,2,8,9,2,5,3,2,5,0,0,1,4,1,0,9,4,6,3,3,2,5,9,4,5,6,4,1,0,4, %U A019699 2,1,8,7,5,0,4,8,2,7,8,6,6,4,8,3,7,3,7,9,7,6,7,1,2,2,8,2,2,7,5 %N A019699 Decimal expansion of 2*Pi/15 = (4*Pi/3)/10. %C A019699 With offset 1, decimal expansion of 4*Pi/3, the volume of a sphere of radius 1. - _Omar E. Pol_, Aug 27 2007, Sep 25 2013 %C A019699 2*Pi/15 is the common value of the base angles of the isosceles triangle formed at the common vertex of the figure obtained by gluing a hexagon and a pentagon, both regular, along a common side, as shown in the CNRS link. - _Michel Marcus_, Mar 06 2015 %C A019699 This is also the surface area (in some cubic length unit (l.u.)) of a sphere with a central cylinder symmetrical hole of length 2 l.u. Thanks to Sven Heinemeyer for reminding me of this classical astonishing result. See e.g., Bild der Wissenschaft, Januar 1964, p. 75, or the Gardner reference, Problem 7 on p. 51. In two dimensions things are different. See A258146. - _Wolfdieter Lang_, May 31 2015 %D A019699 Bild der Wissenschaft, Januar 1964. %D A019699 Martin Gardner, Mathematische Rätsel und Probleme, 3. Auflage, Friedr. Vieweg + Sohn, Braunschweig, 1975, p. 51 (in German). In English: Mathematical Puzzles and Diversions from "Scientific American", Simon and Schuster, N. Y. 1959/1961. %H A019699 Ivan Panchenko, <a href="/A019699/b019699.txt">Table of n, a(n) for n = 0..1000</a> %H A019699 Ana Rechtman, <a href="http://images-archive.math.cnrs.fr/Fevrier-2015-4eme-defi.html">Février 2015, 4ème défi</a>, Images des Mathématiques, CNRS, 2015. %H A019699 <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a> %F A019699 (1/10)*volume of the unit sphere in R^3 = (1/10)*Pi^(3/2)/gamma(1+3/2). - _Benoit Cloitre_, Jun 19 2003 %e A019699 2*Pi/15 = 0.418879020478639098461685784437267... %e A019699 4*Pi/3 = 4.18879020478639098461685784437267... - _Omar E. Pol_, Sep 25 2013 %t A019699 RealDigits[(2 Pi)/15,10,120][[1]] (* _Harvey P. Dale_, Mar 22 2015 *) %o A019699 (PARI) 2*Pi/15 \\ _Charles R Greathouse IV_, Jan 09 2018 %Y A019699 Cf. A000796, A019692, A019693. %K A019699 nonn,cons %O A019699 0,1 %A A019699 _N. J. A. Sloane_