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A031658
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 70.
0
1226, 61553, 99937, 100570, 101842, 150665, 209933, 276901, 356698, 360289, 362693, 363898, 443917, 446585, 449261, 454637, 651778, 659873, 661498, 664754, 768001, 769754, 771509, 773266, 778549, 780314, 782081, 1037165, 1041241, 1045325, 1049417
OFFSET
1,1
MATHEMATICA
cf70Q[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]] == 70]; Select[Range[11 10^5], cf70Q] (* Harvey P. Dale, Jul 24 2017 *)
CROSSREFS
Sequence in context: A218273 A046177 A031748 * A031533 A031713 A259998
KEYWORD
nonn
EXTENSIONS
Corrected and extended and definition clarified by Harvey P. Dale, Jul 24 2017
STATUS
approved