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A156384
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The number of solutions to x^2 + y^2 + 2*z^2 = n in nonnegative integers x,y,z.
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3
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1, 2, 2, 2, 3, 2, 2, 2, 2, 4, 4, 2, 4, 4, 0, 2, 3, 4, 6, 4, 4, 2, 4, 2, 2, 6, 4, 6, 6, 2, 0, 4, 2, 6, 8, 2, 7, 6, 4, 2, 4, 4, 6, 6, 4, 6, 0, 4, 4, 6, 6, 4, 10, 4, 6, 6, 0, 6, 10, 4, 6, 6, 0, 6, 3, 4, 8, 8, 8, 4, 6, 2, 6, 10, 4, 6, 10, 4, 0, 4, 4, 8, 14, 6, 6, 8, 4, 6, 4, 6, 10, 6, 6, 6, 0, 2, 2, 12, 8, 8
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OFFSET
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0,2
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COMMENTS
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Also, the number of 4X4 matrices composed of squares of integers, symmetric under 90 degree rotation, with all rows summing to n. Such matrices have the form:
z^2 x^2 y^2 z^2
y^2 z^2 z^2 x^2
x^2 z^2 z^2 y^2
z^2 y^2 x^2 z^2
with x^2 + y^2 + 2*z^2 = n.
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LINKS
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FORMULA
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G.f.: (1 + theta_3(q))^2*(1 + theta_3(q^2))/8, where theta_3() is the Jacobi theta function. - Ilya Gutkovskiy, Aug 01 2018
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EXAMPLE
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All matrices for n=9:
...0.0.9.0...0.9.0.0...4.0.1.4...4.1.0.4
...9.0.0.0...0.0.0.9...1.4.4.0...0.4.4.1
...0.0.0.9...9.0.0.0...0.4.4.1...1.4.4.0
...0.9.0.0...0.0.9.0...4.1.0.4...4.0.1.4
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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