A089800 - OEIS

A089800

Expansion of Jacobi theta function theta_2(q)/q^(1/4).

2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,1

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..5000

Eric Weisstein's World of Mathematics, Jacobi Theta Functions

I. J. Zucker, Further Relations Amongst Infinite Series and Products. II. The Evaluation of Three-Dimensional Lattice Sums, J. Phys. A: Math. Gen. 23, 117-132, 1990.

FORMULA

For n > 0, a(n) = 2*(floor(sqrt(n+1/4)-1/2) - floor(sqrt(n-1+1/4)-1/2)). - Mikael Aaltonen, Jan 18 2015

a(n) = 2*(floor(sqrt(n+1)+1/2)-floor(sqrt(n)+1/2)). - Mikael Aaltonen, Jan 20 2015

a(n) = 2*A005369(n). - Michel Marcus, Jan 20 2015

MAPLE

A089800 := proc(n)

if issqr(1+4*n) then

if type( sqrt(1+4*n)-1, 'even') then

else

end if;

else

end if;

end proc:

seq( A089800(n), n=0..40) ; # R. J. Mathar, Feb 22 2021

MATHEMATICA

a[n_] := SeriesCoefficient[ EllipticTheta[2, 0, q]/q^(1/4), {q, 0, n}]; Table[a[n], {n, 0, 101}] (* Jean-François Alcover, Nov 12 2012 *)

Table[2*(Floor[Sqrt[n+1]+1/2] - Floor[Sqrt[n]+1/2]), {n, 0, 50}] (* G. C. Greubel, Nov 20 2017 *)

PROG

(PARI) for(n=0, 50, print1(2*(floor(sqrt(n+1)+1/2) - floor(sqrt(n)+1/2)), ", ")) \\ G. C. Greubel, Nov 20 2017

(Magma) [2*(Floor(Sqrt(n+1)+1/2) - Floor(Sqrt(n)+1/2)): n in [0..50]]; // G. C. Greubel, Nov 20 2017

CROSSREFS

Sequence in context: A069517 A193526 A160498 * A079208 A262682 A318983

Adjacent sequences: A089797 A089798 A089799 * A089801 A089802 A089803

KEYWORD

nonn

AUTHOR

Eric W. Weisstein, Nov 12 2003

STATUS

approved