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A071387
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Smallest number k for which the set of solutions to phi(x) = k has 2n-1 entries.
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3
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0, 2, 8, 32, 40, 48, 396, 704, 72, 216, 144, 1056, 360, 384, 1320, 240, 9000, 7128, 480, 1296, 15936, 3072, 864, 7344, 720, 4992, 2016, 6000, 4752, 3024, 9984, 1920, 7560, 22848, 29160, 3360, 13248, 27720, 9072, 9360, 4032, 4800, 16896, 3840, 9504, 23520, 5040
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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) = Min({x; Card(InvPhi(x)) = 2n-1}); a(1)=0 because of Carmichael conjecture.
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EXAMPLE
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For n = 7: 2n-1 = 13, a(7) = Min(InvPhi(13)) = Min({396,400,420,552,560,660}) = 396.
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PROG
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(PARI) a(n) = {if (n==1, return (0)); my(k=1); while(#invphi(k) != 2*n-1, k++); k; } \\ Michel Marcus, May 13 2020
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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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