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A020784 Decimal expansion of 1/sqrt(27). 12
1, 9, 2, 4, 5, 0, 0, 8, 9, 7, 2, 9, 8, 7, 5, 2, 5, 4, 8, 3, 6, 3, 8, 2, 9, 2, 6, 8, 3, 3, 9, 8, 5, 8, 1, 8, 5, 4, 9, 2, 0, 0, 5, 8, 3, 7, 5, 6, 7, 0, 8, 9, 5, 8, 6, 7, 2, 8, 6, 7, 4, 4, 2, 1, 6, 1, 3, 2, 5, 8, 9, 0, 7, 6, 7, 6, 4, 4, 4, 4, 8, 5, 6, 4, 5, 7, 1, 7, 9, 8, 5, 2, 8, 5, 8, 3, 1, 7, 5 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

This is the minimum ripple factor for a third-order Chebyshev filter for which the generalized reflectionless topology needs no negative elements. - Matthew A. Morgan, Oct 18 2017

LINKS

Ivan Panchenko, Table of n, a(n) for n = 0..1000

FORMULA

Equals Sum_{k>=0} binomial(2*k,k) * k/16^k. - Amiram Eldar, Aug 02 2020

EXAMPLE

0.1924500897298752548363829268339858185492005837567089586728674... - Vladimir Joseph Stephan Orlovsky, May 30 2010

MATHEMATICA

RealDigits[1/Sqrt[27], 10, 200][[1]] (* Vladimir Joseph Stephan Orlovsky, May 30 2010 *)

PROG

(PARI) 1/sqrt(27) \\ G. C. Greubel, Feb 15 2018

(MAGMA) 1/Sqrt(27) // G. C. Greubel, Feb 15 2018

CROSSREFS

Sequence in context: A133841 A099769 A176517 * A111188 A334845 A195405

Adjacent sequences:  A020781 A020782 A020783 * A020785 A020786 A020787

KEYWORD

nonn,cons

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified July 23 22:20 EDT 2021. Contains 346265 sequences. (Running on oeis4.)