login
A083721
Number of primes greater than the greatest prime factor of n but not greater than n.
1
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.
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
Sequence in context: A275327 A359677 A215486 * A158459 A319666 A307333
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 04 2003
STATUS
approved