A031545 - OEIS

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A031545

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 47.

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

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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: A031772 A374271 A305880 * A191679 A349098 A238456

Adjacent sequences: A031542 A031543 A031544 * A031546 A031547 A031548

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved