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%I #18 Aug 14 2015 04:00:05
%S 2,2,1,2,1,1,0,1,1,2,1,1,0,1,1,2,1,1,0,1,1,1,0,0,0,1,1,2,1,1,0,0,0,1,
%T 1,1,0,1,1,2,1,1,0,1,1,1,0,0,0,1,1,1,0,0,0,1,1,2,1,1,0,0,0,1,1,1,0,1,
%U 1,2,1,1,0,0,0,1,1,1,0,1,1,1,0,0,0,1,1,1,0,0,0,0,0,1,1,1,0,1,1,2,1,1
%N a(n) = PrimePi(n+3) - PrimePi(n).
%C a(n) <= 2, with equality if and only if n=1 or n+1 is in A001359. - _Robert Israel_, Aug 14 2015
%H Robert Israel, <a href="/A090406/b090406.txt">Table of n, a(n) for n = 1..10000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Hardy-LittlewoodConjectures.html">Hardy-Littlewood Conjectures</a>
%F a(n) = A010051(n+1) + A010051(n+2) + A010051(n+3). - _Robert Israel_, Aug 14 2015
%p B:= [seq(numtheory:-pi(n),n=1..103)]:
%p B[4..-1] - B[1..-4]; # _Robert Israel_, Aug 14 2015
%t Last[#]-First[#]&/@Partition[PrimePi[Range[110]],4,1] (* _Harvey P. Dale_, Feb 24 2013 *)
%Y Cf. A000720, A001359, A010051, A080545, A090405.
%K nonn
%O 1,1
%A _Eric W. Weisstein_, Nov 29 2003
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