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A031645 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 57. 0
40049, 40853, 66130, 67162, 67681, 98717, 188581, 235514, 237458, 238433, 298477, 300665, 365257, 370105, 436129, 440098, 442754, 508994, 510421, 513281, 514714, 516149, 521909, 523354, 524801, 593629, 686425, 703085, 785957, 796625 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
cf57Q[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]]==cf[[(len+1)/2]]==57]; Select[Range[800000], cf57Q] (* Harvey P. Dale, Jan 17 2024 *)
CROSSREFS
Sequence in context: A270261 A272889 A126104 * A250079 A237238 A236253
KEYWORD
nonn
AUTHOR
EXTENSIONS
First term 3250 removed by Georg Fischer, Jun 16 2019
STATUS
approved

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)