A020784 Decimal expansion of 1/sqrt(27).

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

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

References

Steven R. Finch, Mathematical Constants, Encyclopedia of Mathematics and its Applications, vol. 94, Cambridge University Press, 2003, Sections 8.4.3 and 8.16, pp. 495, 527.

Links

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

Index entries for algebraic numbers, degree 2.

Formula

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

Equals sqrt(3)/9. - Stefano Spezia, Dec 24 2024

Equals 1/A010482 = A020760/3 = sqrt(A021031) = A073010/Pi = A212886/2. - Hugo Pfoertner, Dec 24 2024

Example

0.1924500897298752548363829268339858185492005837567089586728674....

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

Cf. A002194, A010482, A020760, A021031, A073010, A212886.

Sequence in context: A133841 A099769 A176517 * A111188 A334845 A195405

Adjacent sequences: A020781 A020782 A020783 * A020785 A020786 A020787

Keyword

nonn,cons,easy

Author

N. J. A. Sloane

Status

approved