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A031545 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 47. 0
2211, 2227, 2231, 2239, 2243, 2251, 2263, 2267, 2283, 2287, 2311, 2339, 2347, 2351, 2363, 2371, 2383, 2399, 8840, 8864, 8872, 8896, 8936, 8960, 9032, 9056, 9088, 9160, 9256, 9320, 9344, 9376, 9440, 9448, 9472, 9512, 9536, 9600, 19887, 19959, 20031 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

MATHEMATICA

cf47Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s] [[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 47]; Select[Range[21000], cf47Q] (* Harvey P. Dale, Apr 07 2018 *)

CROSSREFS

Sequence in context: A300166 A031772 A305880 * A191679 A349098 A238456

Adjacent sequences:  A031542 A031543 A031544 * A031546 A031547 A031548

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified January 22 16:44 EST 2022. Contains 350484 sequences. (Running on oeis4.)