A031643 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 55.

19069, 38074, 61585, 62581, 63082, 129769, 131213, 173281, 219313, 224018, 225914, 279145, 281261, 407573, 413978, 473969, 478106, 479489, 480874, 482261, 485041, 487829, 489226, 560233, 566233, 650477, 728570, 730277, 733697, 737125

Offset

1,1

Links

Table of n, a(n) for n=1..30.

Mathematica

ct55Q[n_]:=Module[{c=ContinuedFraction[Sqrt[n]], len}, len=Length[c[[2]]]; OddQ[len]&&Take[c[[2]], {Floor[len/2], Ceiling[len/2]}]=={55, 55}]; cfsqrtn[ upto_]:=Module[{rng=Complement[ Range[upto], Range[Floor[Sqrt[upto]]]^2]}, Select[rng, ct55Q]]; cfsqrtn[740000] (* Harvey P. Dale, Mar 08 2012 *)

Crossrefs

Sequence in context: A232576 A339962 A235928 * A261748 A089522 A251041

Adjacent sequences: A031640 A031641 A031642 * A031644 A031645 A031646

Keyword

nonn

Author

David W. Wilson

Extensions

Corrected by Harvey P. Dale, Mar 08 2012

Status

approved