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A092308
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For p=prime(n), a(n) = the number of primes q such that q-1 divides p-1.
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2
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1, 2, 3, 3, 3, 5, 4, 4, 3, 4, 5, 7, 5, 4, 3, 4, 3, 8, 5, 4, 8, 4, 3, 5, 7, 5, 4, 3, 8, 6, 6, 4, 4, 5, 4, 6, 8, 5, 3, 4, 3, 11, 4, 8, 5, 7, 8, 4, 3, 6, 5, 3, 11, 4, 5, 3, 4, 7, 8, 8, 4, 4, 6, 4, 9, 4, 8, 10, 3, 7, 7, 3, 4, 6, 7, 3, 4, 11, 8, 8, 4, 13, 4, 11, 4, 3, 7, 7, 6, 7, 3, 3, 6, 5, 5, 3, 4, 8, 6, 14, 6, 4
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| For many primes p, there are only 3 primes (2,3,p) such the q-1|p-1. See A092307 for a list of those primes.
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
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EXAMPLE
| a(12)=7 because for prime(12)=37 there are seven primes q={2, 3, 5, 7, 13, 19, 37} such that q-1 divides 36.
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MATHEMATICA
| Table[p=Prime[n]; Length[Select[Divisors[p-1]+1, PrimeQ]], {n, 150}]
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CROSSREFS
| Cf. A092307 (primes for which a(n)=3).
Sequence in context: A057957 A076559 A102601 * A205394 A205778 A081831
Adjacent sequences: A092305 A092306 A092307 * A092309 A092310 A092311
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KEYWORD
| nonn
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Feb 12 2004
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