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A103710 Decimal expansion of the ratio of the length of the latus rectum arc of any parabola to its semi latus rectum: sqrt(2) + log(1 + sqrt(2)). 9
2, 2, 9, 5, 5, 8, 7, 1, 4, 9, 3, 9, 2, 6, 3, 8, 0, 7, 4, 0, 3, 4, 2, 9, 8, 0, 4, 9, 1, 8, 9, 4, 9, 0, 3, 8, 7, 5, 9, 7, 8, 3, 2, 2, 0, 3, 6, 3, 8, 5, 8, 3, 4, 8, 3, 9, 2, 9, 9, 7, 5, 3, 4, 6, 6, 4, 4, 1, 0, 9, 6, 6, 2, 6, 8, 4, 1, 3, 3, 1, 2, 6, 6, 8, 4, 0, 9, 4, 4, 2, 6, 2, 3, 7, 8, 9, 7, 6, 1, 5, 5, 9, 1, 7, 5 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The universal parabolic constant, equal to the ratio of the latus rectum arc of any parabola to its focal parameter. Like Pi, it is transcendental.

Just as all circles are similar, all parabolas are similar. Just as the ratio of a semicircle to its radius is always Pi, the ratio of the latus rectum arc of any parabola to its semi latus rectum is sqrt(2) + log(1 + sqrt(2)).

Note the remarkable similarity to sqrt(2) - log(1 + sqrt(2)), the universal equilateral hyperbolic constant A222362, which is a ratio of areas rather than of arc lengths. Lockhart (2012) says "the arc length integral for the parabola .. is intimately connected to the hyperbolic area integral ... I think it is surprising and wonderful that the length of one conic section is related to the area of another."

Is it a coincidence that the universal parabolic constant is equal to 6 times the expected distance A103712 from a randomly selected point in the unit square to its center? (Reese, 2004; Finch, 2012)

REFERENCES

H. Dörrie, 100 Great Problems of Elementary Mathematics, Dover, 1965, Problems 57 and 58.

P. Lockhart, Measurement, Harvard University Press, 2012, p. 369.

C. E. Love, Differential and Integral Calculus, 4th ed., Macmillan, 1950, pp. 286-288.

C. S. Ogilvy, Excursions in Geometry, Oxford Univ. Press, 1969, p. 84.

S. Reese, A universal parabolic constant, 2004, preprint.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..10000

J. L. Diaz-Barrero and W. Seaman, A limit computed by integration, Problem 810 and Solution, College Math. J., 37 (2006), 316-318, equation (5).

S. R. Finch, Mathematical Constants, Errata and Addenda, 2012, section 8.1.

Hamza Khelif, L’arbelos, Partie II, Généralisations de l’arbelos, Images des Mathématiques, CNRS, 2014.

J. Pahikkala, Arc Length Of Parabola, PlanetMath.

S. Reese, Pohle Colloquium Video Lecture: The universal parabolic constant, Feb 02 2005

S. Reese, J. Sondow, Eric W. Weisstein, MathWorld: Universal Parabolic Constant

J. Sondow, The parbelos, a parabolic analog of the arbelos, arXiv 2012, Amer. Math. Monthly 120 (2013) 929-935.

Emmanuel Tsukerman, Solution of Sondow's problem: a synthetic proof of the tangency property of the parbelos, arXiv 2012.

Wikipedia, Universal parabolic constant

EXAMPLE

2.29558714939263807403429804918949038759783220363858348392997534664...

MATHEMATICA

RealDigits[ Sqrt[2] + Log[1 + Sqrt[2]], 10, 111][[1]] (* Robert G. Wilson v Feb 14 2005 *)

PROG

(Maxima) fpprec: 100$ ev(bfloat(sqrt(2) + log(1 + sqrt(2)))); /* Martin Ettl, Oct 17 2012 */

(PARI) sqrt(2)+log(1+sqrt(2)) \\ Charles R Greathouse IV, Mar 08 2013

CROSSREFS

A002193 + A091648.

Cf. A103711, A103712, A222362, A232716, A232717.

Sequence in context: A157216 A020776 A021002 * A178236 A093589 A073315

Adjacent sequences:  A103707 A103708 A103709 * A103711 A103712 A103713

KEYWORD

cons,easy,nonn

AUTHOR

Sylvester Reese and Jonathan Sondow, Feb 13 2005

STATUS

approved

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Last modified April 20 17:21 EDT 2014. Contains 240807 sequences.