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a(n) = -PrimePi(n) +floor( prime(n)/log(n))-2.
3

%I #7 May 15 2013 08:00:20

%S 1,0,1,1,2,2,3,4,6,5,7,7,8,9,11,11,12,12,13,13,15,15,17,19,19,20,21,

%T 20,21,23,24,26,26,28,29,29,30,31,32,33,33,34,35,35,35,37,40,41,41,42,

%U 43,42,44,46,47,48,48,48,49,48,50,54,54,54,55,57,58,60,61,60,61,62,63,64

%N a(n) = -PrimePi(n) +floor( prime(n)/log(n))-2.

%F a(n) = A085581(n)-A000720(n) -2. - _R. J. Mathar_, May 15 2013

%p A087724 := proc(n)

%p floor( ithprime(n)/log(n))-numtheory[pi](n) -2 ;

%p end proc: # _R. J. Mathar_, May 15 2013

%t Digits=200 a[n_]=-PrimePi[n]+Floor[Prime[n]/Log[n]]-2 b=Table[a[n], {n, 2, Digits}]

%K nonn

%O 2,5

%A _Roger L. Bagula_, Sep 29 2003