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A084196
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Number of primes q<prime(n) such that q+1 divides prime(n)+1.
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6
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0, 0, 1, 1, 3, 0, 2, 1, 5, 2, 2, 0, 3, 1, 6, 3, 6, 0, 1, 7, 0, 3, 6, 4, 1, 2, 2, 6, 0, 3, 3, 5, 2, 3, 3, 3, 0, 1, 9, 2, 9, 1, 8, 0, 3, 3, 1, 4, 6, 0, 3, 11, 0, 8, 2, 8, 6, 3, 0, 2, 1, 5, 3, 7, 0, 2, 1, 0, 5, 1, 2, 13, 2, 0, 3, 10, 3, 0, 2, 0, 11, 0, 11, 2, 5, 5, 6, 0, 4, 2, 6, 13, 2, 5, 2, 13, 4, 4, 1, 0, 1, 4
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OFFSET
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1,5
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COMMENTS
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LINKS
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EXAMPLE
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n=5, prime(5)=11: (11+1) mod (q+1) = 0 for 3 primes q<11: 2, 3,
and 5, therefore a(5)=3.
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MATHEMATICA
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Table[Count[Mod[p+1, Prime[Range[PrimePi[p]-1]]+1], 0], {p, Prime[Range[110]]}] (* Harvey P. Dale, Aug 11 2023 *)
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PROG
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(Haskell)
a084196 n = a084196_list !! (n-1)
a084196_list = f [] a000040_list where
f ps' (p:ps) = length [q | q <- ps', mod (p + 1) (q + 1) == 0] :
f (p : ps') ps where
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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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