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A020837 Decimal expansion of 1/sqrt(80) = sqrt(5)/20. 8
1, 1, 1, 8, 0, 3, 3, 9, 8, 8, 7, 4, 9, 8, 9, 4, 8, 4, 8, 2, 0, 4, 5, 8, 6, 8, 3, 4, 3, 6, 5, 6, 3, 8, 1, 1, 7, 7, 2, 0, 3, 0, 9, 1, 7, 9, 8, 0, 5, 7, 6, 2, 8, 6, 2, 1, 3, 5, 4, 4, 8, 6, 2, 2, 7, 0, 5, 2, 6, 0, 4, 6, 2, 8, 1, 8, 9, 0, 2, 4, 4, 9, 7, 0, 7, 2, 0, 7, 2, 0, 4, 1, 8, 9, 3, 9, 1, 1, 3 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Multiplied by 100, this is sqrt(125). - Alonso del Arte, Jan 06 2013

Multiplied by 10, this is sqrt(5)/2. As such, it appears in the Pythagorean tree as the ratio of the distance between 2 consecutive square centers divided by the length of the initial square (see CNRS link). - Michel Marcus, Feb 20 2013

The two-dimensional Steinitz constant K_2(0,0), related to sum of vectors, is sqrt(5)/2. - Jean-François Alcover, Jun 04 2014

REFERENCES

Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.13 Steinitz constants, p. 241.

LINKS

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

Étienne Ghys and Jos Leys, Un arbre pythagoricien — Images des Mathématiques, CNRS, 2013.

FORMULA

1/sqrt(80) = sqrt(5)/20 = (-1 + 2*phi)/20, with phi from A001622.

EXAMPLE

sqrt(5)/20 = 0.111803398874989484820458683436563811772...

sqrt(5)/2  = 1.118033988749894848204586834365638117720...

MATHEMATICA

RealDigits[1/Sqrt[80], 10, 120][[1]] (* Harvey P. Dale, May 01 2012 *)

PROG

(PARI) sqrt(1/80) \\ Charles R Greathouse IV, Apr 25 2016

CROSSREFS

c = (1/10)*(A001622 - 1/2) = (1/10)*(7/2 - A079585).

Sequence in context: A144455 A251866 A300713 * A248679 A175574 A195342

Adjacent sequences:  A020834 A020835 A020836 * A020838 A020839 A020840

KEYWORD

nonn,cons

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified April 9 23:09 EDT 2020. Contains 333382 sequences. (Running on oeis4.)