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A008451
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Number of ways of writing n as a sum of 7 squares.
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18
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1, 14, 84, 280, 574, 840, 1288, 2368, 3444, 3542, 4424, 7560, 9240, 8456, 11088, 16576, 18494, 17808, 19740, 27720, 34440, 29456, 31304, 49728, 52808, 43414, 52248, 68320, 74048, 68376, 71120, 99456, 110964, 89936, 94864, 136080, 145222
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,2
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REFERENCES
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E. Grosswald, Representations of Integers as Sums of Squares. Springer-Verlag, NY, 1985, p. 121.
G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, p. 314.
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LINKS
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Shi-Chao Chen, Congruences for rs(n), Journal of Number Theory, Volume 130, Issue 9, September 2010, Pages 2028-2032.
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FORMULA
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G.f.: theta_3(0,x)^7, where theta_3 is the third Jacobi theta function. - Robert Israel, Jul 16 2014
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MAPLE
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series((sum(x^(m^2), m=-10..10))^7, x, 101);
# Alternative
#(requires at least Maple 17, and only works as long as a(n) <= 10^16 or so):
N:= 1000: # to get a(0) to a(N)
with(SignalProcessing):
A:= Vector(N+1, datatype=float[8], i-> piecewise(i=1, 1, issqr(i-1), 2, 0)):
A2:= Convolution(A, A)[1..N+1]:
A4:= Convolution(A2, A2)[1..N+1]:
A5:= Convolution(A, A4)[1..N+1];
A7:= Convolution(A2, A5)[1..N+1];
# Alternative
A008451list := proc(len) series(JacobiTheta3(0, x)^7, x, len+1);
seq(coeff(%, x, j), j=0..len-1) end: A008451list(37); # Peter Luschny, Oct 02 2018
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MATHEMATICA
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Table[SquaresR[7, n], {n, 0, 36}] (* Ray Chandler, Nov 28 2006 *)
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PROG
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(Sage)
Q = DiagonalQuadraticForm(ZZ, [1]*7)
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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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