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A086685
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Number of 1<=i<n such that i*n+1 is prime.
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0
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0, 1, 1, 2, 1, 4, 2, 2, 3, 5, 3, 6, 4, 5, 5, 5, 3, 10, 2, 6, 6, 9, 4, 9, 5, 9, 7, 11, 4, 17, 3, 10, 9, 12, 9, 15, 4, 9, 11, 13, 5, 21, 7, 11, 10, 16, 8, 19, 6, 18, 13, 17, 5, 23, 10, 18, 9, 16, 8, 27, 7, 15, 13, 16, 13, 29, 9, 18, 13, 27, 9, 26, 10, 19, 18, 17, 11, 29, 11, 23, 18, 22, 11, 32
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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EXAMPLE
| For n=10, i=1,3,4,6,7 give primes, so a(10)=5
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MATHEMATICA
| f[n_] := Length[ Select[ Range[n - 1], PrimeQ[n# + 1] & ]]; Table[ f[n], {n, 1, 85}]
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PROG
| (PARI) nphi(n)=local(c); c=0; for (i=1, n-1, if (isprime(i*n+1), c++)); c for(i=1, 60, print1(", "nphi(i)))
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CROSSREFS
| Sequence in context: A161822 A001176 A136693 * A094571 A104733 A201703
Adjacent sequences: A086682 A086683 A086684 * A086686 A086687 A086688
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KEYWORD
| nonn
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AUTHOR
| Jon Perry (perry(AT)globalnet.co.uk), Jul 28 2003
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EXTENSIONS
| Extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Jul 31 2003
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