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A031656
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 68.
0
29609, 57649, 94330, 94945, 96181, 141497, 143005, 262369, 336689, 420265, 422861, 425465, 515965, 521725, 524617, 621473, 724826, 728234, 729941, 733361, 735074, 738506, 743669, 847129, 850813, 988877, 992857, 1113986, 1118210
OFFSET
1,1
MATHEMATICA
cf68Q[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]] == 68]; Select[Range[1200, 112*10^4], cf68Q] (* Harvey P. Dale, Jan 27 2020 *)
CROSSREFS
Sequence in context: A251563 A022200 A234669 * A236734 A236317 A204601
KEYWORD
nonn
EXTENSIONS
First term 4625 removed by Georg Fischer, Jun 16 2019
Definition modified by Harvey P. Dale, Jan 27 2020
STATUS
approved