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A072530
Number of primes p such that n divided by p leaves a prime remainder.
7
0, 0, 0, 0, 1, 0, 1, 2, 1, 1, 1, 2, 2, 2, 1, 3, 3, 3, 2, 3, 1, 3, 3, 5, 2, 4, 2, 4, 3, 4, 3, 4, 4, 3, 2, 6, 4, 5, 2, 6, 4, 6, 3, 6, 4, 5, 5, 7, 4, 6, 4, 5, 4, 8, 3, 5, 4, 7, 5, 9, 3, 7, 5, 8, 5, 7, 3, 8, 4, 8, 5, 10, 6, 7, 5, 8, 4, 9, 6, 9, 7, 8, 4, 10, 5, 7, 6, 8, 7, 12, 5, 8, 8, 8, 5, 12, 6, 10, 5, 10, 5
OFFSET
1,8
COMMENTS
Is there any n > 6 such that a(n) =0 ?
EXAMPLE
a(17) = 3: there are 3 primes viz. 3, 5 and 7 which leave prime remainders on dividing 17.
MATHEMATICA
Table[Count[PrimeQ[Table[Mod[w, Prime[j]], {j, 1, PrimePi[w]}]], True], {w, 1, 256}]
CROSSREFS
Cf. A072531.
Sequence in context: A109700 A087742 A340996 * A184341 A090455 A273190
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Aug 01 2002
EXTENSIONS
More terms from Labos Elemer, Aug 02 2002
STATUS
approved