A048862 - OEIS

A048862

Number of primes in the reduced residue system of n-th primorial number (=A002110(n)).

0, 0, 1, 7, 42, 338, 3242, 42324, 646021, 12283522, 300369786, 8028642999, 259488750732, 9414916809082, 362597750396726, 15397728527812843, 742238179058722875, 40068968501510691877, 2251262473052300960808, 139566579945945392719394

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OFFSET

0,4

LINKS

Table of n, a(n) for n=0..19.

Kim Walisch, Fast C++ prime counting function implementation (primecount).

FORMULA

a(n) = A000849(n) - n = A000720(A002110(n)) - A001221(A002110(n)).

EXAMPLE

For n = 3, the 3rd primorial is 30, phi(30) = 8, a(3) = 8-1 = 7 since 1 is nonprime. See A048597.

For n = 4, the 4th primorial is 210, the size of its reduced residue system (RRS) is 48 of which 42 are primes and 6 are either composite numbers or 1.

CROSSREFS

Cf. A000010 (phi), A000720, A000849, A001221, A002110, A007625, A048597, A048863.

Sequence in context: A073506 A025593 A218124 * A208943 A209071 A174224

Adjacent sequences: A048859 A048860 A048861 * A048863 A048864 A048865

KEYWORD

more,nonn

AUTHOR

Labos Elemer

EXTENSIONS

a(0) prepended and extended by Max Alekseyev, Feb 22 2016

a(17) corrected and a(18)-a(19) calculated using Kim Walisch's primecount and added by Amiram Eldar, Sep 03 2024

STATUS

approved