%I #7 Mar 14 2018 13:35:22
%S 421,463,541,571,613,661,673,718,719,739,763,764,814,821,883,921,937,
%T 956,981,1061,1081,1099,1117,1121,1125,1135,1174,1237,1249,1252,1270,
%U 1390,1413,1423,1441,1459,1468,1477,1511,1583,1651,1657,1661,1676,1723,1724
%N Period of continued fraction for sqrt(n) contains exactly 16 ones.
%t cf16Q[n_]:=Module[{s=Sqrt[n]},If[IntegerQ[s],1,Count[ ContinuedFraction[ s][[2]],1]]==16]; Select[Range[2000],cf16Q] (* _Harvey P. Dale_, Mar 14 2018 *)
%K nonn
%O 1,1
%A _David W. Wilson_