A083721 Number of primes greater than the greatest prime factor of n but not greater than n.

0, 0, 0, 1, 0, 1, 0, 3, 2, 1, 0, 3, 0, 2, 3, 5, 0, 5, 0, 5, 4, 3, 0, 7, 6, 3, 7, 5, 0, 7, 0, 10, 6, 4, 7, 9, 0, 4, 6, 9, 0, 9, 0, 9, 11, 5, 0, 13, 11, 12, 8, 9, 0, 14, 11, 12, 8, 6, 0, 14, 0, 7, 14, 17, 12, 13, 0, 12, 10, 15, 0, 18, 0, 9, 18, 13, 16, 15, 0, 19, 20, 9, 0, 19, 16, 9, 13, 18, 0, 21, 18

Offset

1,8

Comments

a(n) = A000720(n) - A000720(A006530(n));

a(n) > 0 if and only if n is composite.

Links

Table of n, a(n) for n=1..91.

Prog

(PARI) a(n)=if(n>3, my(f=factor(n)[, 1]); primepi(n)-primepi(f[#f]), 0) \\ Charles R Greathouse IV, Feb 21 2013

Crossrefs

Cf. A083722, A079067.

Sequence in context: A275327 A359677 A215486 * A158459 A319666 A307333

Adjacent sequences: A083718 A083719 A083720 * A083722 A083723 A083724

Keyword

nonn

Author

Reinhard Zumkeller, May 04 2003

Status

approved