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A131232 a(n) = number of positive integers < n which don't have 2 or more distinct prime divisors in common with n. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 24 06:53 EST 2020. Contains 338607 sequences. (Running on oeis4.)