%I A105149
%S A105149 0,1,1,2,1,2,2,2,1,3,2,3,3,2,4,2,3,3,4,5,1,6,3,5,3,4,4,5,4,6,5,5,3,6,5,
%T A105149 7,6,4,6,5,7,6,5,6,6,8,8,5,6,8,7,6,5,9,9,7,10,6,7,8,5,10,6,10,9,8,8,10,
%U A105149 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 A105149 Number of even semiprimes k such that n^2 < k <= (n+1)^2.
%C A105149 a(n)>=1 because there is always a number 2*prime(i) between n^2 and (n+1)^2 
               for n>0.
%e A105149 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.
%t A105149 f[n_] := PrimePi[Floor[n^2/2]]; Table[f[(n + 1)] - f[n], {n, 0, 100}]
%Y A105149 Cf. A105148.
%Y A105149 Sequence in context: A023588 A001227 A060764 this_sequence A068307 A158946 
               A023645
%Y A105149 Adjacent sequences: A105146 A105147 A105148 this_sequence A105150 A105151 
               A105152
%K A105149 easy,nonn
%O A105149 0,4
%A A105149 Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Apr 10 2005
%E A105149 Edited and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), 
               Apr 16 2005