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A307616
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a(n) is the smallest k with the property that i / gcd(i, k) is a prime power (or 1) for i = 1..n.
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4
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1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 4, 4, 4, 6, 6, 6, 6, 6, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 120, 120, 120, 120, 120, 120, 120, 360, 360, 360, 360, 360, 360, 360
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OFFSET
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1,6
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COMMENTS
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LINKS
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MATHEMATICA
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A307616[x_]:=(For[i=1, Length[Select[PrimeNu[Range[x]/GCD[Range[x], i]], #>1&]]>0, i++]; i)
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PROG
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(PARI) ispp(k) = (k==1) || isprimepower(k);
isok(k, n) = {for (i=1, n, if (! ispp(i/gcd(i, k)), return (0); )); return (1); }
a(n) = my(k=1); while (! isok(k, n), k++); k; \\ Michel Marcus, Jun 11 2019
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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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