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%I #3 Mar 30 2012 17:30:44
%S 4,57,664,7068,73130,747244,7590269
%N Number of k's less than or equal to 10^n such that there are no middle divisors of k (A071090).
%t f[n_] := Plus @@ Select[ Divisors[n], Sqrt[n/2] <= # < Sqrt[n*2] &]; s = 0; k = 0; Do[ While[k < 10^n, k++; If[ f[k] == 0, s++ ]]; Print[s], {n, 1, 7}]
%Y Cf. A071541.
%K nonn
%O 1,1
%A _Robert G. Wilson v_, May 31 2002
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