A031623 Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 35.

15178, 25681, 38537, 52153, 53069, 53993, 70981, 72586, 90289, 91493, 115961, 137341, 140317, 164554, 166993, 168629, 170273, 171098, 192469, 193346, 195989, 196874, 197761, 201329, 229213, 258905, 260941, 262985, 265037, 267097, 271241

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Crossrefs

Subsequence of A003814.

Programs

Mathematica

ct35Q[n_]:=Module[{s=Sqrt[n],cf,len,ctr},If[IntegerQ[s],cf={1,1},cf= ContinuedFraction[ s][[2]]];len=Length[cf];ctr=Floor[len/2];OddQ[len] && Take[cf,{ctr,ctr+1}]=={35,35}]; Select[Range[280000],ct35Q] (* Harvey P. Dale, Apr 16 2013 *)

Extensions

Corrected by Harvey P. Dale, Apr 16 2013