A031541 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 43.

1851, 1867, 1871, 1879, 1899, 1907, 1923, 1927, 1931, 1951, 1979, 1987, 1999, 2003, 2011, 2023, 7400, 7424, 7488, 7520, 7528, 7552, 7584, 7592, 7624, 7680, 7712, 7720, 7776, 7808, 7872, 7880, 7904, 7976, 8000, 8032, 8096, 16647, 16707, 16719, 16791

Offset

1,1

Links

Table of n, a(n) for n=1..41.

Mathematica

cf43Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 43]; Select[Range[17000], cf43Q] (* Harvey P. Dale, Jan 08 2019 *)

Crossrefs

Sequence in context: A206468 A031764 A031674 * A031721 A224567 A303272

Adjacent sequences: A031538 A031539 A031540 * A031542 A031543 A031544

Keyword

nonn

Author

David W. Wilson

Extensions

Definition corrected by Harvey P. Dale, Feb 24 2023

Status

approved