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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A031521 Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 23. 0
 531, 547, 563, 571, 587, 599, 603, 607, 619, 623, 2120, 2144, 2152, 2176, 2216, 2240, 2344, 2368, 2432, 2440, 2496, 4767, 4839, 4911, 4983, 5055, 5127, 5199, 5271, 5487, 5547, 5619, 8472, 8664, 8728, 8856, 8984, 9112, 9304, 9352, 9368, 9432, 9496, 9624 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The "central term" is the term that appears at 1/2 the length of the period of the continued fraction. - Harvey P. Dale, Feb 25 2012 LINKS Table of n, a(n) for n=1..44. MATHEMATICA cf2Q[n_]:=Module[{cf=ContinuedFraction[Sqrt[n]], len}, If[Length[cf]==1, len=1, len=Length[cf[[2]]]]; EvenQ[len]&&cf[[2, len/2]]==23]; Select[ Range[10000], cf2Q](* Harvey P. Dale, Feb 26 2012 *) CROSSREFS Sequence in context: A174761 A031967 A345387 * A156772 A031701 A158367 Adjacent sequences: A031518 A031519 A031520 * A031522 A031523 A031524 KEYWORD nonn AUTHOR David W. Wilson EXTENSIONS Definition edited by Harvey P. Dale, Jun 08 2023 STATUS approved

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.

Last modified October 2 20:27 EDT 2023. Contains 365840 sequences. (Running on oeis4.)