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A045848
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Number of nonnegative solutions of x1^2 + x2^2 + ... + x6^2 = n.
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7
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1, 6, 15, 20, 21, 36, 61, 60, 45, 72, 120, 120, 95, 120, 186, 200, 141, 150, 270, 300, 216, 252, 375, 360, 271, 306, 450, 500, 390, 396, 626, 660, 405, 420, 735, 780, 582, 600, 825, 920, 720, 606, 960, 1140, 825
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OFFSET
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0,2
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LINKS
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FORMULA
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Coefficient of q^n in (1 + q + q^4 + q^9 + q^16 + q^25 + q^36 + q^49 + q^64 + ...)^6.
G.f.: (1 + theta_3(q))^6/64, where theta_3() is the Jacobi theta function. - Ilya Gutkovskiy, Aug 08 2018
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MATHEMATICA
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(1 + EllipticTheta[3, 0, q])^6/64 + O[q]^45 // CoefficientList[#, q]& (* Jean-François Alcover, Aug 26 2019 *)
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PROG
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(PARI) seq(n)=Vec((sum(k=0, sqrtint(n), x^(k^2)) + O(x*x^n))^6) \\ Andrew Howroyd, Aug 08 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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