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A048866
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Difference between number of nonprimes and primes in reduced residue system of n.
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1
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1, 1, 0, 0, 0, 0, 0, -2, 0, 0, 2, -2, 2, -2, 0, -2, 4, -4, 4, -4, 0, -2, 6, -6, 4, -2, 2, -2, 10, -6, 10, -4, 2, -2, 6, -6, 14, -2, 4, -4, 16, -8, 16, -4, 0, -2, 18, -10, 14, -6, 6, -2, 22, -10, 12, -4, 8, 0, 26, -12, 26, -2, 4, -2, 16, -10, 30, -2, 10, -8, 32, -12, 32, -2, 2, -2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,8
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EXAMPLE
| n = 31: Phi(31) = 30 from which 10 is prime and 20 is not: a(31) = 20-10 = 10; n = 20: Phi(20) = 8 from which 6 are primes and 2 are not: a(20) = 2-6 = -4; n = 15: reduced residue system = {1,2,7,4,8,11,13,14}, primes = {2,7,11,13,}, nonprimes = {2,4,8,14}, thus a(15) = 4-4 = 0.
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CROSSREFS
| A000010(n) - 2*A000720(n) + 2* A001221(n))
Sequence in context: A029361 A107502 A146165 * A138527 A144377 A033718
Adjacent sequences: A048863 A048864 A048865 * A048867 A048868 A048869
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KEYWORD
| sign
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu)
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