This site is supported by donations to The OEIS Foundation.

"Email this user" was broken Aug 14 to 9am Aug 16. If you sent someone a message in this period, please send it again.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A272490 Decimal expansion of the edge length of a regular 13-gon with unit circumradius. 7
 4, 7, 8, 6, 3, 1, 3, 2, 8, 5, 7, 5, 1, 1, 5, 5, 3, 4, 2, 9, 7, 5, 0, 7, 4, 5, 2, 5, 2, 0, 4, 2, 3, 7, 9, 0, 4, 0, 6, 3, 4, 6, 0, 4, 5, 4, 7, 6, 6, 1, 2, 0, 2, 6, 7, 1, 0, 3, 1, 9, 4, 3, 7, 3, 2, 3, 6, 6, 3, 1, 2, 5, 7, 0, 1, 5, 0, 3, 7, 4, 3, 9, 2, 2, 3, 8, 9, 9, 6, 4, 4, 4, 1, 7, 2, 8, 8, 9, 4, 5, 1, 7, 9, 4, 6 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The edge length e(m) of a regular m-gon is e(m) = 2*sin(Pi/m). In this case, m = 13, and the constant, a = e(13), is not constructible using a compass and a straightedge (see A004169). With an odd m, in fact, e(m) would be constructible only if m were a Fermat prime (A019434). LINKS Stanislav Sykora, Table of n, a(n) for n = 0..2000 Wikipedia, Constructible number Wikipedia, Regular polygon FORMULA Equals 2*sin(Pi/13) = 2*cos(Pi*11/26). EXAMPLE 0.47863132857511553429750745252042379040634604547661202671031943... MATHEMATICA RealDigits[N[2Sin[Pi/13], 100]][[1]] (* Robert Price, May 01 2016 *) PROG (PARI) 2*sin(Pi/13) CROSSREFS Cf. A004169, A019434. Edge lengths of nonconstructible n-gons: A271487 (n=7), A272488 (n=9), A272489 (n=11), A255241 (n=14), A130880 (n=18), A272491 (n=19). Sequence in context: A154687 A115021 A200367 * A261654 A121488 A115291 Adjacent sequences:  A272487 A272488 A272489 * A272491 A272492 A272493 KEYWORD nonn,cons,easy AUTHOR Stanislav Sykora, May 01 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.