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Number of primes <= n is equal to the sum of squarefree numbers from the smallest prime factor of n to the largest prime factor of n.
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%I #7 Dec 15 2017 17:36:01

%S 1,4,12,30,84,9150,47244,75360,177287,281868,705790,3043504,9669715,

%T 20139930,32043111,67447484,291217662,7544909388,8396469108,

%U 21425170627

%N Number of primes <= n is equal to the sum of squarefree numbers from the smallest prime factor of n to the largest prime factor of n.

%e pi(84) = 23 and 84 = 2^2*3*7 and 2+3+5+6+7 = 23.

%Y Cf. A000720.

%K more,nonn

%O 0,2

%A _Jason Earls_, Sep 20 2002

%E a(6)-a(19) from _Donovan Johnson_, Oct 12 2008