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%I #3 Mar 30 2012 18:50:42
%S 0,0,0,4,8,16,32,64,192,384,768,1536,3072,6144,12288,24576,49152,
%T 98304,196608,393216,786432,1572864,3145728,6291456,10485760,20971520,
%U 41943040,83886080,167772160,335544320,671088640,1342177280
%N Number of subsets of {1,.., n} containing exactly two squares.
%C a(n) = A000217(A000196(n)-1)*A089887(n);
%C for n>2: a(n) = A089886(n,2).
%F a(n) = (n^(1/2)*(n^(1/2)-1)*2^(n-n^(1/2)))/2.
%Y Cf. A089889.
%K nonn
%O 1,4
%A _Reinhard Zumkeller_, Nov 13 2003