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A051762 Polygon circumscribing constant: decimal expansion of Product_{n=3..infinity} 1/cos(Pi/n). 6
8, 7, 0, 0, 0, 3, 6, 6, 2, 5, 2, 0, 8, 1, 9, 4, 5, 0, 3, 2, 2, 2, 4, 0, 9, 8, 5, 9, 1, 1, 3, 0, 0, 4, 9, 7, 1, 1, 9, 3, 2, 9, 7, 9, 4, 9, 7, 4, 2, 8, 9, 2, 0, 9, 2, 1, 5, 9, 6, 6, 7, 2, 7, 8, 6, 8, 3, 4, 2, 9, 9, 6, 4, 1, 1, 4, 0, 2, 5, 1, 5, 9, 1, 1, 8, 5, 4, 4, 4, 1, 4, 0, 0, 9, 2, 4, 9, 5, 2, 8, 5, 5 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The geometric interpretation is as follows. Begin with a unit circle. Circumscribe an equilateral triangle and then circumscribe a circle. Circumscribe a square and then circumscribe a circle. Circumscribe a regular pentagon and then circumscribe a circle, etc. The circles have radius which converges to this value.

Grimstone corrects an error in other references and gives an approximation for 1/A085365, see there for further information. - M. F. Hasler, May 18 2014

REFERENCES

Clifford A. Pickover, The Math Book, From Pythagoras to the 57th Dimension, 250 Milestones in the History of Mathematics, Sterling Publ., NY, 2009, page 382.

LINKS

Table of n, a(n) for n=1..102.

M. Chamberland, A. Straub, On Gamma quotients and infinite products, arXiv:1309.3455, Section 4.

Clive J. Grimstone, A product of cosines, Math. Gaz. 64 (428) (1980) 120-121.

A. R. Kitson, The prime analog of the Kepler-Bouwkamp constant, arXiv:math/0608186.

R. J. Mathar, Tightly circumscribed regular polygons, arXiv:1301.6293 [math.MG]

Kival Ngaokrajang, Illustration of polygon inscribing

Eric Weisstein's World of Mathematics, Polygon Circumscribing

Wikipedia, Polygon circumscribing constant

FORMULA

A051762 = 1/A085365.

EXAMPLE

= 8.700036625208194503222409844942662399362013328900933610030879474...

MATHEMATICA

RealDigits[ N[ Product[ 1 / Cos[Pi/n], {n, 3, Infinity}], 111]] [[1]]

(* A check of the calculation can be made by dividing the product into two halves as follows: *)

a = N[Product[1/Cos[Pi/(2 n + 1)], {n, 1, Infinity}], 111]

(* = 3.739103623800432767390049906937236355729731994887558649737... *)

b = N[Product[1/Cos[Pi/(2 n)], {n, 2, Infinity}], 111]

(* = 2.3267706649877381643146528716336217838145696941... and a*b = A051762. - Robert G. Wilson v, Dec 22 2013 *)

PROG

(PARI) exp(-sumpos(n=3, log(cos(Pi/n)))) \\ Converges very quickly, which is not the case for suminf(...) or prodinf(cos(Pi/n)). - M. F. Hasler, May 18 2014

CROSSREFS

Cf. A085365, A118253, A131671, A211174.

Sequence in context: A058088 A112145 A038284 * A247017 A198112 A213007

Adjacent sequences:  A051759 A051760 A051761 * A051763 A051764 A051765

KEYWORD

nonn,cons

AUTHOR

Robert G. Wilson v, Aug 23 2000

EXTENSIONS

More terms from Eric W. Weisstein, Jun 25 2003

Edited by M. F. Hasler, May 18 2014

STATUS

approved

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Last modified September 20 03:54 EDT 2014. Contains 246983 sequences.