A131232 - OEIS

%I #7 Apr 09 2014 10:15:03

%S 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,

%T 26,26,28,22,30,31,32,33,34,30,36,37,38,36,40,32,42,42,42,45,46,40,48,

%U 45,50,50,52,45,54,52,56,57,58,44,60,61,60,63,64,52,66,66,68,58,70,60,72

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

%e 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.

%Y Cf. A131233.

%K nonn

%O 1,3

%A _Leroy Quet_, Jun 20 2007

%E More terms from _Joshua Zucker_, Jul 18 2007