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A071387
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Smallest number for which InvPhi-Set has 2n-1 entries.
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1
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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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Table of n, a(n) for n=1..47.
Max Alekseyev, PARI scripts for various problems (see invphi.gp there).
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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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2n-1 = 13: Min{396,400,420,552,560,660} = 396 = a(7).
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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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Cf. A000010, A014197, A058277, A063512, A071386, A071388, A071389.
Sequence in context: A279692 A332444 A323145 * A330782 A200063 A238984
Adjacent sequences: A071384 A071385 A071386 * A071388 A071389 A071390
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KEYWORD
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nonn
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AUTHOR
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Labos Elemer, May 23 2002
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EXTENSIONS
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a(12)-a(47) from Donovan Johnson, Jul 27 2011
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STATUS
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approved
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