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Number of numbers m <= n with prime factors less than 2*spf(m), where spf(m) is the smallest prime factor of m (A020639).
2

%I #3 Mar 30 2012 18:50:31

%S 1,2,3,4,5,6,7,8,9,9,10,11,12,12,13,14,15,16,17,17,17,17,18,19,20,20,

%T 21,21,22,22,23,24,24,24,25,26,27,27,27,27,28,28,29,29,30,30,31,32,33,

%U 33,33,33,34,35,35,35,35,35,36,36,37,37,37,38,38,38,39,39,39,39,40,41,42

%N Number of numbers m <= n with prime factors less than 2*spf(m), where spf(m) is the smallest prime factor of m (A020639).

%C a(n)+A081305(n)=n; a(114)=A081305(114)=57;

%C a(n)>=n/2 for n<=114, a(n)<n/2 for n>114.

%Y Cf. A081306, A081303.

%K nonn

%O 1,2

%A _Reinhard Zumkeller_, Mar 17 2003