A131232 a(n) = number of positive integers < n which don't have 2 or more distinct prime divisors in common with n.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 12, 13, 14, 15, 16, 15, 18, 18, 20, 21, 22, 20, 24, 25, 26, 26, 28, 22, 30, 31, 32, 33, 34, 30, 36, 37, 38, 36, 40, 32, 42, 42, 42, 45, 46, 40, 48, 45, 50, 50, 52, 45, 54, 52, 56, 57, 58, 44, 60, 61, 60, 63, 64, 52, 66, 66, 68, 58, 70, 60, 72

Offset

1,3

Links

Table of n, a(n) for n=1..73.

Example

The distinct primes which divide 20 are 2 and 5. So a(20) is the number of positive integers < 20 which are not divisible by at least 2 distinct primes dividing 20; i.e. are not divisible by both 2 and 5. Among the first 19 positive integers only 10 is divisible by both 2 and 5. There are 18 other positive integers <= 19, so a(20)=18.

Crossrefs

Cf. A131233.

Sequence in context: A017895 A228722 A130024 * A297238 A010881 A190600

Adjacent sequences: A131229 A131230 A131231 * A131233 A131234 A131235

Keyword

nonn

Author

Leroy Quet, Jun 20 2007

Extensions

More terms from Joshua Zucker, Jul 18 2007

Status

approved