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A219428
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a(n) = n - 1 - phi(n).
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4
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-1, 0, 0, 1, 0, 3, 0, 3, 2, 5, 0, 7, 0, 7, 6, 7, 0, 11, 0, 11, 8, 11, 0, 15, 4, 13, 8, 15, 0, 21, 0, 15, 12, 17, 10, 23, 0, 19, 14, 23, 0, 29, 0, 23, 20, 23, 0, 31, 6, 29, 18, 27, 0, 35, 14, 31, 20, 29, 0, 43, 0, 31, 26, 31, 16, 45, 0, 35, 24, 45, 0, 47
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OFFSET
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1,6
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COMMENTS
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Apart from the first term, the same as A016035.
For n > 1, a(n) is also the number of numbers below n which are not coprime to n.
a(n) = 0 if n is prime.
x^(n - 1 - phi(n)) is congruent to x^(n - 1) mod n, if x is coprime to n, since x^phi(n) is congruent to 1 (mod n) if x is coprime to n.
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LINKS
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FORMULA
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MATHEMATICA
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PROG
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(PARI) for(n=1, 100, print1(n-1-eulerphi(n)", "))
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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STATUS
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approved
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