OFFSET
1,3
COMMENTS
Entry 34 a of chapter 11 of Ramanujan's second notebook. Entry 34 b is A085565.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..5000
Bruce C. Berndt, Chapter 11 of Ramanujan's second notebook, Bull. Lond. Math. Soc., Vol. 15, No. 4 (1983), 273-320.
Wikipedia, Theta function.
FORMULA
Equals Sum_{n=-oo..oo} exp(-Pi*n^2), or also EllipticTheta(3, 0, exp(-Pi)). - Jean-François Alcover, Jul 04 2013
Equals sqrt(A175574). - Amiram Eldar, Jul 04 2023
Equals Gamma(1/4)/(sqrt(2)*Pi^(3/4)). - Vaclav Kotesovec, Jul 04 2023
Equals Product_{k>=1} tanh((1/2 + i/2)*Pi*k), i=sqrt(-1). - _Antonio Graciá Llorente, Mar 20 2024
Equals Product_{k>=0} (1/2)*(((k+1/2)/(k+1))^(1/2)+((k+1)/(k+1/2))^(1/2)). - Antonio Graciá Llorente, Jul 23 2024
EXAMPLE
1.0864348112133080145753161...
MAPLE
Pi^(1/4)/GAMMA(3/4) ; evalf(%) ;
MATHEMATICA
RealDigits[ Pi^(1/4)/Gamma[3/4], 10, 105][[1]] (* Jean-François Alcover, Jul 04 2013 *)
PROG
(PARI) Pi^(1/4)/gamma(3/4) \\ G. C. Greubel, Nov 05 2017
(PARI) 2*suminf(k=0, exp(-Pi)^(k^2))-1 \\ Hugo Pfoertner, Sep 17 2018
(Magma) C<i> := ComplexField(); [(Pi(C))^(1/4)/Gamma(3/4)]; // G. C. Greubel, Nov 05 2017
CROSSREFS
KEYWORD
AUTHOR
R. J. Mathar, Jul 15 2010
STATUS
approved