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%I #10 Oct 31 2013 12:17:13
%S 13,21,31,57,61,67,73,74,92,106,108,109,111,112,116,129,137,158,161,
%T 162,183,185,193,204,207,236,237,243,246,251,261,262,265,273,274,275,
%U 282,297,298,308,314,317,329,332,341,346,351,355,364,375,381,383,384,388,406,412
%N Period of continued fraction for sqrt(n) contains exactly four 1's.
%t Select[ Range@ 1900, !IntegerQ[ Sqrt@ #] && Count[ ContinuedFraction[ Sqrt@ #][[2]], 1] == 4 &] (* _Robert G. Wilson v_, Jul 03 2011 *)
%K nonn
%O 1,1
%A _David W. Wilson_
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