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A031661
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 73.
0
12109, 66098, 109642, 110305, 163337, 306034, 387173, 388418, 390914, 393418, 394673, 481997, 484777, 596425, 709493, 719633, 723029, 841514, 845186, 850709, 852554, 854401, 1124441, 1137197, 1145741, 1298282, 1300561, 1457938, 1460353, 1489489
OFFSET
1,1
MATHEMATICA
cf73Q[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]]==73]; Select[Range[15*10^5], cf73Q] (* Harvey P. Dale, Oct 10 2017 *)
CROSSREFS
Sequence in context: A008914 A257357 A070187 * A371952 A247403 A262635
KEYWORD
nonn
EXTENSIONS
Corrected and extended and definition clarified by Harvey P. Dale, Oct 10 2017
STATUS
approved