Search: a066900 -id:a066900
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A066899
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a(n) = card({k : phi(k) == n (mod k)}).
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+10
1
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1, 3, 1, 4, 2, 5, 1, 7, 2, 3, 2, 7, 2, 5, 2, 7, 2, 5, 2, 10, 2, 3, 3, 15, 2, 3, 2, 5, 3, 3, 1, 12, 4, 5, 2, 9, 2, 7, 2, 12, 3, 7, 2, 8, 4, 3, 2, 16, 2, 5, 3, 4, 4, 9, 2, 10, 2, 3, 4, 12, 2, 5, 2, 15, 3, 3, 2, 9, 5, 5, 2, 20, 2, 5, 3, 8, 3, 5, 2, 15, 2, 3, 5, 12, 2
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OFFSET
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1,2
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COMMENTS
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Note that k=1 is excluded from the count. - Michel Marcus, Feb 22 2021
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LINKS
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PROG
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(PARI) a(n) = {my(v = invphi(n), m = if (#v, vecmax(v), n)); sum(i=2, m, Mod(eulerphi(i), i) == n); } \\ Michel Marcus, Feb 22 2021; needs invphi.gp
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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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