A069998 - OEIS

A069998

Decimal expansion of sqrt(Pi/2).

1, 2, 5, 3, 3, 1, 4, 1, 3, 7, 3, 1, 5, 5, 0, 0, 2, 5, 1, 2, 0, 7, 8, 8, 2, 6, 4, 2, 4, 0, 5, 5, 2, 2, 6, 2, 6, 5, 0, 3, 4, 9, 3, 3, 7, 0, 3, 0, 4, 9, 6, 9, 1, 5, 8, 3, 1, 4, 9, 6, 1, 7, 8, 8, 1, 7, 1, 1, 4, 6, 8, 2, 7, 3, 0, 3, 9, 2, 0, 9, 8, 7, 4, 7, 3, 2, 9, 7, 9, 1, 9, 1, 8, 9, 0, 2, 8, 6, 3, 3, 0, 5, 8, 0, 0, 4

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OFFSET

1,2

COMMENTS

This constant, sqrt(Pi/2), appears in one of the formulations of the Birthday Problem: An asymptotic expansion of the expected value for the average number of people required to find a pair having the same birthday out of k possible birthdays is sqrt(Pi/2)*sqrt(k) + 2/3 + 1/12*sqrt(Pi/2)*sqrt(1/k) - 4/135*1/k + ... found by the Indian mathematician Srinivasa Ramanujan (1887-1920). - Martin Renner, Sep 14 2016

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5000

P. Flajolet, P. J. Grabner, P. Kirschenhofer and H. Prodinger, On Ramanujan's Q-Function, Journal of Computational and Applied Mathematics 58 (1995), 103-116.

I. S. Gradsteyn and I. M. Ryzhik, Table of integrals, series and products, (1980), page 420 (formulas 3.757.1, 3.757.2).

Index entries for transcendental numbers

FORMULA

From A.H.M. Smeets, Sep 22 2018: (Start)

Equals Integral_{x >= 0} sin(x)/sqrt(x) dx [see Gradsteyn and Ryzhik].

Equals Integral_{x >= 0} cos(x)/sqrt(x) dx [see Gradsteyn and Ryzhik]. (End)

Equals Integral_{x>=0} (sin(x)-x*cos(x))/x^(3/2) dx. - Amiram Eldar, May 08 2021

EXAMPLE

Sqrt(Pi/2) = 1.253314137315500251207882642... - Wesley Ivan Hurt, Sep 22 2016

MAPLE

Digits:=100: evalf(sqrt(Pi/2)); # Wesley Ivan Hurt, Sep 22 2016

MATHEMATICA