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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
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
FORMULA
Equals Sum_{k>=0} binomial(2*k,k) * k/16^k. - Amiram Eldar, Aug 02 2020
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
Sequence in context: A133841 A099769 A176517 * A111188 A334845 A195405
KEYWORD
nonn,cons
STATUS
approved