A031665 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 77.

72949, 120490, 121882, 122581, 179897, 252173, 337786, 340114, 341281, 433253, 435889, 438533, 663037, 792629, 796193, 797978, 801554, 927994, 933781, 935714, 943466, 945409, 947354, 949301, 1086493, 1107433, 1250765, 1255241

Offset

1,1

Links

Table of n, a(n) for n=1..28.

Mathematica

cf77Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1, 1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; OddQ[len]&&cf[[(len+1)/2]] == 77]; Select[Range[1255300], cf77Q] (* Harvey P. Dale, Mar 30 2019 *)

Crossrefs

Sequence in context: A254582 A254589 A254357 * A247993 A210009 A237701

Adjacent sequences: A031662 A031663 A031664 * A031666 A031667 A031668

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected by Harvey P. Dale, Mar 30 2019

Status

approved