A048980 - OEIS

A048980

Difference between number of nonprimes and primes in reduced residue system of primorial numbers.

1, 1, 0, -6, -36, -196, -724, 7512, 366838, 11928316, 421130508, 14598816402, 584642184936, 25314953837836, 1128885572358548, 54492272309366314, 2950485568862138250, 213151926413154110951

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OFFSET

0,4

LINKS

Table of n, a(n) for n=0..17.

FORMULA

a(n) = A048863(n) - A048862(n) = A048866(A002110(n)).

a(n) = A005867(n) - 2*A000849(n) + 2*n.

EXAMPLE

n=4, Q(4)=2*3*5*7=210, reduced residue system includes 48 terms:42 primes and 6 composites and 1: a(4)=6-42=-36.

MATHEMATICA

Table[Function[P, EulerPhi@ P - 2 # &[PrimePi@ P - n]]@ Product[Prime@ i, {i, n}], {n, 0, 12}] (* Michael De Vlieger, May 08 2017 *)

CROSSREFS

Cf. A048868, A048867, A048597, A002110, A048862, A048863, A048866.

Sequence in context: A106539 A215453 A267229 * A200782 A055299 A261520

Adjacent sequences: A048977 A048978 A048979 * A048981 A048982 A048983

KEYWORD

sign

AUTHOR

Labos Elemer

EXTENSIONS

Corrected and extended by Max Alekseyev, Feb 22 2016

STATUS

approved