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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

%I #17 Aug 18 2021 00:10:32

%S 1226,61553,99937,100570,101842,150665,209933,276901,356698,360289,

%T 362693,363898,443917,446585,449261,454637,651778,659873,661498,

%U 664754,768001,769754,771509,773266,778549,780314,782081,1037165,1041241,1045325,1049417

%N 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.

%t 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 *)

%K nonn

%O 1,1

%A _David W. Wilson_

%E Corrected and extended and definition clarified by _Harvey P. Dale_, Jul 24 2017

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Last modified May 29 22:39 EDT 2023. Contains 363044 sequences. (Running on oeis4.)