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A366723
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a(n) = Sum_{k=1..n} (-1)^(k-1) * binomial(floor(n/k)+4,5).
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4
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1, 5, 21, 50, 121, 236, 447, 736, 1247, 1896, 2898, 4151, 5972, 8146, 11292, 14797, 19643, 25248, 32564, 40663, 51515, 63168, 78119, 94452, 114998, 136933, 164849, 193753, 229714, 268334, 314711, 362824, 422746, 483950, 558046, 635070, 726461, 820420, 934186, 1048245
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = Sum_{k=1..n} binomial(k+3,4) * (floor(n/k) mod 2).
G.f.: -1/(1-x) * Sum_{k>=1} (-x)^k/(1-x^k)^5 = 1/(1-x) * Sum_{k>=1} binomial(k+3,4) * x^k/(1+x^k).
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PROG
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(PARI) a(n) = sum(k=1, n, (-1)^(k-1)*binomial(n\k+4, 5));
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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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