A083721 - OEIS

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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

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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.