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A281867
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Number of sets of exactly seven positive integers <= n having a square element sum.
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2
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0, 0, 4, 10, 25, 60, 124, 238, 435, 750, 1237, 1973, 3047, 4574, 6706, 9624, 13546, 18742, 25533, 34292, 45469, 59585, 77238, 99127, 126048, 158897, 198713, 246663, 304057, 372374, 453245, 548479, 660104, 790372, 941770, 1117035, 1319141, 1551314, 1817124
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OFFSET
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7,3
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LINKS
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EXAMPLE
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a(9) = 4: {1,2,3,6,7,8,9}, {1,2,4,5,7,8,9}, {1,3,4,5,6,8,9}, {2,3,4,5,6,7,9}.
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MAPLE
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b:= proc(n, i, t) option remember;
`if`(i<t, 0, `if`(n=0, `if`(t=0, 1, 0),
`if`(t<1 or n<t*(t+1)/2 or n>(t+1)*(2*i-t)/2, 0,
`if`(i>n, 0, b(n-i, i-1, t-1))+b(n, i-1, t))))
end:
a:= proc(n) option remember; `if`(n<0, 0, a(n-1)+add(
b(j^2-n, n-1, 6), j=isqrt(n-21)..isqrt(7*n-21)))
end:
seq(a(n), n=7..60);
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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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