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A031675
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 87.
0
94298, 153745, 155317, 156106, 430561, 434506, 547889, 550853, 555314, 689261, 692585, 695917, 839497, 846841, 1010554, 1014578, 1184369, 1190906, 1193089, 1195274, 1201841, 1204034, 1206229, 1208426, 1388413, 1603597, 1608665
OFFSET
1,1
MATHEMATICA
cf87Q[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]] == 87]; Select[Range[1610000], cf87Q] (* Harvey P. Dale, Mar 25 2016 *)
CROSSREFS
Sequence in context: A029754 A258892 A204473 * A254977 A238143 A110845
KEYWORD
nonn
EXTENSIONS
Definition clarified and terms corrected by Harvey P. Dale, Mar 25 2016
STATUS
approved