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A361695
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Number of ways of writing n^2 as a sum of seven squares.
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2
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1, 14, 574, 3542, 18494, 43414, 145222, 235998, 591934, 860846, 1779974, 2256422, 4678982, 5195750, 9675918, 10983742, 18942014, 19873966, 35294686, 34670454, 57349894, 59707494, 92513302, 90116222, 149759302, 135668414, 213025750, 209185718, 311753358, 287144326, 450333422
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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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a(n) = [x^(n^2)] (Sum_{j=-n..n} x^(j^2))^7.
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MAPLE
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a:= n-> coeff((sum(x^(j^2), j=-n..n))^7, x, n^2):
seq(a(n), n=0..30);
# second Maple program:
b:= proc(n, t) option remember; `if`(n=0, 1, `if`(n<0 or t<1, 0,
b(n, t-1) +2*add(b(n-j^2, t-1), j=1..isqrt(n))))
end:
a:= n-> b(n^2, 7):
seq(a(n), n=0..30);
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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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