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A066676
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Smallest number m such that phi(m) is a multiple of n-th primorial number, the product of first n primes.
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6
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3, 7, 31, 211, 2311, 60653, 1023053, 19417793, 446235509, 12939711677, 200560490131, 14841484883609, 608500576478849, 26165522997357677, 1229779567395958169, 65178316970529225209, 3845520700432469775917, 234576762719782814756597, 15716643102168462956621849
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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n = 8: a(8) = 19417793, phi(a(8)) = 19199380 = 2*9699690 = 2*2*3*5*7*11*13*17*19.
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MATHEMATICA
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nmax = 25;
pm = 1;
Do[
pm *= Prime[n];
sol = 0;
If[PrimeQ[pm + 1],
sol = pm + 1;
,
sd = Select[Divisors[pm/2], # <= Sqrt[pm/2] &];
Do[
f1 = sd[[i]];
f2 = pm/2/f1;
If[PrimeQ[2 f1 + 1] && PrimeQ[2 f2 + 1],
sol = (2 f1 + 1)*(2 f2 + 1);
Break[];
];
, {i, Length[sd], 1, -1}];
];
Print[{n, sol}];
, {n, nmax}];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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