A217219 - OEIS

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A217219

Theta series of planar hexagonal net (honeycomb) with respect to deep hole.

0, 6, 0, 0, 6, 0, 0, 12, 0, 0, 0, 0, 0, 12, 0, 0, 6, 0, 0, 12, 0, 0, 0, 0, 0, 6, 0, 0, 12, 0, 0, 12, 0, 0, 0, 0, 0, 12, 0, 0, 0, 0, 0, 12, 0, 0, 0, 0, 0, 18, 0, 0, 12, 0, 0, 0, 0, 0, 0, 0, 0, 12, 0, 0, 6, 0, 0, 12, 0, 0, 0, 0, 0, 12, 0, 0, 12, 0, 0, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 24, 0, 0, 0, 0, 0, 12, 0, 0, 6, 0, 0, 12, 0

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OFFSET

0,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..2500

N. J. A. Sloane, Theta series and magic numbers for diamond and certain ionic crystal structures, J. Math. Phys. 28 (1987), 1653-1657.

FORMULA

See A033685, A045833.

a(n) = 2*A033685(n) = 6*A045833(n).

Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 4*Pi/(3*sqrt(3)) = 2.418399... (A275486). - Amiram Eldar, Oct 13 2022

MATHEMATICA

terms = 105; s = 6 q QPochhammer[q^9]^3/QPochhammer[q^3] + O[q]^(terms+5); CoefficientList[s, q][[1 ;; terms]] (* Jean-François Alcover, Jul 06 2017, after Michael Somos *)

CoefficientList[Series[6 q QPochhammer[q^9]^3/QPochhammer[q^3], {q, 0, 100}], q] (* G. C. Greubel, Aug 10 2018 *)

PROG

(PARI) my(q='q+O('q^100)); concat([0], Vec(6*q*eta(q^9)^3/eta(q^3))) \\ G. C. Greubel, Aug 10 2018

CROSSREFS

Cf. A033685, A045833, A275486.

Sequence in context: A114760 A261508 A344182 * A113555 A066604 A081550

Adjacent sequences: A217216 A217217 A217218 * A217220 A217221 A217222

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Oct 05 2012

EXTENSIONS

Name edited by Andrey Zabolotskiy, Jun 21 2022

STATUS

approved