A072530 Number of primes p such that n divided by p leaves a prime remainder.

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 ?

Links

Table of n, a(n) for n=1..101.

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

Adjacent sequences: A072527 A072528 A072529 * A072531 A072532 A072533

Keyword

nonn

Author

Amarnath Murthy, Aug 01 2002

Extensions

More terms from Labos Elemer, Aug 02 2002

Status

approved