A072531 Number of primes p such that n divided by p leaves a 1 or a composite (nonzero) remainder.

0, 0, 1, 1, 1, 1, 2, 1, 2, 1, 3, 1, 3, 2, 3, 2, 3, 2, 5, 3, 5, 3, 5, 2, 6, 3, 6, 3, 6, 3, 7, 6, 5, 6, 7, 3, 7, 5, 8, 4, 8, 4, 10, 6, 8, 7, 9, 6, 10, 7, 9, 8, 11, 6, 11, 9, 10, 7, 11, 5, 14, 9, 11, 9, 11, 8, 15, 9, 13, 8, 14, 8, 14, 12, 14, 11, 15, 9, 15, 11, 14, 12, 18, 10, 16, 14, 15, 13, 16, 9

Offset

1,7

Links

Table of n, a(n) for n=1..90.

Example

a(7) = 2: there are 2 primes viz. 2,3 which leave a remainder 1 on dividing 7.

Mathematica

Table[Count[PrimeQ[DeleteCases[Table[Mod[w, Prime[j]], {j, 1, PrimePi[w]}], 0]], False], {w, 1, 256}]

Crossrefs

Cf. A072530.

Sequence in context: A126131 A343332 A138012 * A025818 A324938 A362181

Adjacent sequences: A072528 A072529 A072530 * A072532 A072533 A072534

Keyword

nonn

Author

Amarnath Murthy, Aug 01 2002

Extensions

More terms from Labos Elemer, Aug 02 2002

Status

approved