A085341 Number of primes between sigma(n) and n.

0, 1, 0, 2, 0, 2, 0, 2, 2, 3, 0, 4, 0, 3, 3, 5, 0, 5, 0, 5, 3, 3, 0, 8, 2, 4, 3, 7, 0, 10, 0, 7, 4, 5, 4, 13, 0, 5, 4, 12, 0, 11, 0, 9, 7, 6, 0, 15, 1, 9, 5, 10, 0, 14, 4, 14, 6, 8, 0, 22, 0, 6, 9, 13, 5, 16, 0, 11, 5, 15, 0, 24, 0, 9, 9, 13, 3, 18, 0, 20, 8

Offset

1,4

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Formula

a(n) = pi(sigma(n)) - pi(n) = A000720(A000203(n)) - A000720(n).

Example

n = 12: sigma(n) = 28, pi(28) - pi(12) = 9 - 5 = 4.

Mathematica

Table[PrimePi[DivisorSigma[1, n]]-PrimePi[n], {n, 90}] (* Harvey P. Dale, Aug 18 2015 *)

Prog

(PARI) a(n) = primepi(sigma(n)) - primepi(n); \\ Michel Marcus, Dec 15 2013

Crossrefs

Cf. A000720, A000203, A070803, A070804, A085342-A085347.

Sequence in context: A161840 A355851 A140302 * A221474 A160812 A338271

Adjacent sequences: A085338 A085339 A085340 * A085342 A085343 A085344

Keyword

nonn

Author

Labos Elemer, Jul 10 2003

Status

approved