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A366123
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The number of prime factors of the cube root of the largest cube dividing n, counted with multiplicity.
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1
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0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0
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OFFSET
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1,64
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COMMENTS
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First differs from A295659 at n = 64.
The number of distinct prime factors of the cube root of the largest cube dividing n is A295659(n).
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LINKS
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FORMULA
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Additive with a(p^e) = floor(e/3) = A002264(e).
a(n) >= 0, with equality if and only if n is cubefree (A004709).
a(n) <= A001222(n)/3, with equality if and only if n is a positive cube (A000578 \ {0}).
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = Sum_{p prime} 1/(p^3-1) = 0.194118... (A286229).
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MATHEMATICA
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f[p_, e_] := Floor[e/3]; a[1] = 0; a[n_] := Plus @@ f @@@ FactorInteger[n]; Array[a, 100]
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PROG
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(PARI) a(n) = vecsum(apply(x -> x\3, factor(n)[, 2]));
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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