login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A031616 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 28. 0

%I #16 Aug 18 2021 00:10:32

%S 5209,16210,16465,16981,24457,35513,45169,46021,58853,59338,60314,

%T 72185,74345,75437,92857,106154,107458,108113,110753,123826,124529,

%U 125941,127361,128074,128789,131669,151273,168941,170585,172237,173897

%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 28.

%t cf28Q[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]] == 28]; Rest[Select[Range[174000],cf28Q]] (* _Harvey P. Dale_, Jun 24 2020 *)

%Y Subsequence of A003814.

%K nonn

%O 1,1

%A _David W. Wilson_

%E First term 785 removed by _Georg Fischer_, Jun 16 2019

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 23 22:36 EDT 2024. Contains 371917 sequences. (Running on oeis4.)