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%I #8 Feb 05 2018 02:54:17
%S 0,1,1,2,1,2,2,2,1,3,2,3,3,2,4,2,3,3,4,5,1,6,3,5,3,4,4,5,4,6,5,5,3,6,
%T 5,7,6,4,6,5,7,6,5,6,6,8,8,5,6,8,7,6,5,9,9,7,10,6,7,8,5,10,6,10,9,8,8,
%U 10,8,11,5,9,9,13,10,9,9,9,8,8,10,12,7,11,12,12,10,10,12,10,12,10,10,10,11
%N Number of even semiprimes k such that n^2 < k <= (n+1)^2.
%C a(n)>=1 because there is always a number 2*prime(i) between n^2 and (n+1)^2 for n>0.
%H Robert Israel, <a href="/A105149/b105149.txt">Table of n, a(n) for n = 0..9999</a>
%e a(6)=2 because between 5^2 and 6^2 there are two 2*prime(i): 2*prime(6)=2*13 and 2*prime(7)=2*17.
%p L:= map(numtheory:-pi, [seq(floor(n^2/2),n=0..100)]):
%p L[2..-1]-L[1..-2]; # _Robert Israel_, Feb 04 2018
%t f[n_] := PrimePi[Floor[n^2/2]]; Table[f[(n + 1)] - f[n], {n, 0, 100}]
%Y Cf. A105148.
%K easy,nonn
%O 0,4
%A _Giovanni Teofilatto_, Apr 10 2005
%E Edited and extended by _Ray Chandler_, Apr 16 2005
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