login
A031520
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 22.
0
486, 498, 502, 514, 526, 534, 542, 562, 566, 574, 1092, 1101, 1119, 1137, 1149, 1191, 1209, 1236, 1257, 1263, 1281, 1293, 1940, 1948, 1964, 1972, 1996, 2012, 2036, 2044, 2060, 2076, 2084, 2092, 2108, 2124, 2132, 2140, 2156, 2164, 2188, 2204, 2220, 2228
OFFSET
1,1
MATHEMATICA
cf22Q[n_]:=Module[{s=Sqrt[n], cf, len}, cf=If[IntegerQ[s], {1}, ContinuedFraction[ s][[2]]]; len=Length[cf]; EvenQ[len]&&cf[[len/2]] == 22]; Select[Range[2300], cf22Q] (* Harvey P. Dale, Jul 07 2020 *)
CROSSREFS
Sequence in context: A156774 A031632 A097767 * A235525 A249227 A130181
KEYWORD
nonn
STATUS
approved