

A063084


a(n) = pi(n1)*n  pi(n)*(n1), where pi() = A000720().


1



0, 1, 1, 2, 2, 3, 3, 4, 4, 4, 6, 5, 7, 6, 6, 6, 10, 7, 11, 8, 8, 8, 14, 9, 9, 9, 9, 9, 19, 10, 20, 11, 11, 11, 11, 11, 25, 12, 12, 12, 28, 13, 29, 14, 14, 14, 32, 15, 15, 15, 15, 15, 37, 16, 16, 16, 16, 16, 42, 17, 43, 18, 18, 18, 18, 18, 48, 19, 19, 19, 51, 20, 52, 21, 21, 21, 21, 21, 57, 22, 22, 22, 60, 23, 23
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OFFSET

1,4


COMMENTS

To define as positive sequence let C(n)= A062298; f(a) = pi(a) if a is nonprime, f(a)= C(a) if a is prime.  Daniel Tisdale, Nov 07 2008


REFERENCES

G. A. Kudrevatow, (1970): Exercises in Number Theory. Problem 488; page 56; Prosveshenie, Moscow [in Russian].


LINKS

Harry J. Smith, Table of n, a(n) for n = 1..1000


EXAMPLE

The function is positive for composite and negative for prime numbers. It is zero at n=1.


PROG

(PARI) a(n)={if(n>1, primepi(n1)*n  primepi(n)*(n1), 0)} \\ Harry J. Smith, Aug 17 2009


CROSSREFS

Cf. A000720, A000027, A010051, A061397, A000040, A002808.
Sequence in context: A132924 A076890 A103358 * A127079 A080251 A220032
Adjacent sequences: A063081 A063082 A063083 * A063085 A063086 A063087


KEYWORD

sign


AUTHOR

Labos Elemer, Aug 06 2001


STATUS

approved



