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A188618 Decimal expansion of (diagonal)/(shortest side) of 1st electrum rectangle. 4
1, 6, 9, 2, 9, 3, 3, 9, 6, 3, 2, 0, 8, 3, 8, 1, 8, 0, 7, 3, 0, 6, 2, 9, 6, 0, 3, 2, 1, 5, 5, 5, 9, 6, 2, 2, 3, 0, 5, 9, 1, 0, 3, 1, 2, 5, 6, 1, 4, 3, 7, 6, 4, 6, 7, 0, 6, 9, 4, 2, 7, 3, 9, 1, 6, 6, 2, 0, 3, 9, 5, 7, 7, 3, 0, 2, 1, 5, 6, 7, 4, 5, 5, 9, 2, 7, 8, 3, 1, 5, 3, 7, 9, 6, 5, 8, 6, 5, 7, 4, 1, 2, 0, 0, 2, 0, 0, 2, 8, 4, 4, 6, 4, 5, 9, 5, 8, 7, 0, 2, 9, 6, 6, 9, 5, 0, 3, 4, 7, 1 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The 1st electrum rectangle is introduced here as a rectangle whose length L and width W satisfy L/W=(1+sqrt(3))/2.  The name of this shape refers to the alloy of gold and silver known as electrum, in view of the existing names "golden rectangle" and "silver rectangle" and these continued fractions:

golden ratio: L/W=[1,1,1,1,1,1,1,1,1,1,1,...]

silver ratio: L/W=[2,2,2,2,2,2,2,2,2,2,2,...]

1st electrum ratio: L/W=[1,2,1,2,1,2,1,2,...]

2nd electrum ratio: L/W=[2,1,2,1,2,1,2,1,...].

Recall that removal of 1 square from a golden rectangle leaves a golden rectangle, and that removal of 2 squares from a silver rectangle leaves a silver rectangle.  Removal of a square from a 1st electrum rectangle leaves a silver rectangle; removal of 2 squares from a 2nd electrum rectangle leaves a golden rectangle.

LINKS

Table of n, a(n) for n=1..130.

Clark Kimberling, A Visual Euclidean Algorithm, The Mathematics Teacher 76 (1983) 108-109.

FORMULA

(diagonal)/(shortest side) = sqrt(2+(1/2)sqrt(3)).

EXAMPLE

(diagonal)/(shortest side) = 1.6929339632083818 approximately.

MATHEMATICA

h=(1+3^(1/2))/2; (* continued fraction: h=[1, 2, 1, 2, ...].

r=(1+h^2)^(1/2)

FullSimplify[r]

N[r, 130]

RealDigits[N[r, 130]][[1]]

CROSSREFS

Cf. A188593 (golden), A121601 (silver), A188619 (2nd electrum).

Sequence in context: A198616 A215668 A010502 * A225125 A181852 A129938

Adjacent sequences:  A188615 A188616 A188617 * A188619 A188620 A188621

KEYWORD

nonn,cons

AUTHOR

Clark Kimberling, Apr 06 2011

STATUS

approved

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Last modified October 22 18:39 EDT 2014. Contains 248400 sequences.