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A243823
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Quantity of "semitotatives," numbers m < n that are products of at least one prime divisor p of n and one prime q coprime to n.
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22
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0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 3, 3, 4, 0, 3, 0, 5, 5, 6, 0, 6, 3, 8, 6, 9, 0, 5, 0, 11, 8, 11, 7, 11, 0, 13, 10, 14, 0, 12, 0, 16, 14, 17, 0, 18, 5, 19, 14, 20, 0, 21, 11, 22, 16, 23, 0, 19, 0, 25, 20, 26, 13, 25, 0, 27, 20, 27, 0, 31, 0, 30, 27, 31, 13, 32, 0, 35, 23, 34, 0, 33, 17, 36, 25, 38, 0, 35, 15, 39, 27, 40, 19, 45, 0, 44, 32, 46
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OFFSET
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1,14
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COMMENTS
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Semitotatives m < n have a regular factor that is the product of prime divisors of n, and a coprime factor that is the product of primes q that are coprime to n.
The unit fractions of semitotatives have a mixed recurrent expansion in base n (See Hardy & Wright).
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REFERENCES
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G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, Sixth Edition, Oxford University Press, 2008, pages 144-145 (last part of Theorem 136).
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LINKS
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FORMULA
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EXAMPLE
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For n = 10 with prime divisors {2, 5} and prime totatives {3, 7}, the only semitotative is 6. For n = 16, with the prime divisor 2 and the prime totatives {3, 5, 7, 11, 13}, there are four semitotatives {6, 10, 12, 14}.
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MAPLE
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f:= n -> n + 1 - numtheory:-phi(n) - add(numtheory:-mobius(k)*floor(n/k), k=select(t -> igcd(n, t)=1, [$1..n])):
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MATHEMATICA
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Table[n + 1 - EulerPhi@ n - Total[MoebiusMu[#] Floor[n/#] &@ Select[Range@ n, CoprimeQ[#, n] &]], {n, 120}] (* Michael De Vlieger, May 10 2016 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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