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%I #17 Jul 22 2013 16:27:45
%S 4,9,16,18,25,36,49,50,64,72,75,81,98,100,121,144,147,150,162,169,196,
%T 200,225,242,245,256,288,289,294,300,324,338,361,363,392,400,441,450,
%U 484,490,507,529,576,578,588,600,605,625,648,675,676,722,726,729,735
%N Numbers n for which the exponent of the largest prime factor of n is even.
%C What is the density of these numbers? It's clear that lim a(n)/n^2 = 0.
%H Charles R Greathouse IV, <a href="/A195212/b195212.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[800],EvenQ[FactorInteger[#][[-1,2]]]&] (* _Harvey P. Dale_, Jul 22 2013 *)
%o (PARI) is(n)=if(n<4,0,n=factor(n)[,2];n[#n]%2==0) \\ _Charles R Greathouse IV_, Sep 14 2011
%Y Contains the squares, A000290, as a subsequence (apart from 0 and 1).
%K nonn
%O 1,1
%A _Charles R Greathouse IV_, Sep 13 2011