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A181830
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The number of positive integers <= n that are strongly prime to n.
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10
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0, 1, 0, 0, 0, 1, 0, 2, 2, 2, 1, 6, 2, 6, 4, 4, 4, 11, 4, 12, 6, 6, 6, 18, 6, 12, 9, 14, 8, 22, 6, 22, 14, 14, 12, 20, 8, 27, 16, 20, 12, 32, 10, 34, 18, 18, 16, 42, 14, 32, 17, 26, 20, 46, 16, 32, 20, 28, 24, 54, 14, 48, 28, 32, 26, 41, 16
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OFFSET
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0,8
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COMMENTS
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k is strongly prime to n iff k is relatively prime to n and k does not divide n-1.
a(n) = phi(n) - tau(n-1) if n > 0 and a(0) = 0.
Here phi(n) = A000010(n) and tau(n) = A000005(n).
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LINKS
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Table of n, a(n) for n=0..66.
Peter Luschny, Strong coprimality.
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EXAMPLE
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a(11) = card({1,2,3,4,5,6,7,8,9,10} - {1,2,5,10}) = card({3,4,6,7,8,9}) = 6.
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MAPLE
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with(numtheory):
A181830 := n -> `if`(n=0, 0, phi(n)-tau(n-1)):
StrongCoprimes := n -> select(k->igcd(k, n)=1, {$1..n}) minus divisors(n-1):
A181830a := n -> nops(StrongCoprimes(n)):
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CROSSREFS
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Cf. A181831, A181832, A181833, A181834, A181835, A181836, A000010, A000005.
Sequence in context: A184242 A109978 A114293 * A086612 A128207 A180958
Adjacent sequences: A181827 A181828 A181829 * A181831 A181832 A181833
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KEYWORD
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nonn
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AUTHOR
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Peter Luschny, Nov 17 2010
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STATUS
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approved
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