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 A107997 Squarefree integers m congruent to 5 modulo 8 such that the minimal solution of the Pell equation x^2 - m*y^2 = +-4 has both x and y odd. 3
 5, 13, 21, 29, 53, 61, 69, 77, 85, 93, 109, 133, 149, 157, 165, 173, 181, 205, 213, 221, 229, 237, 253, 277, 285, 293, 301, 309, 317, 341, 357, 365, 397, 413, 421, 429, 437, 445, 453, 461, 469, 493, 501, 509, 517, 533, 541, 565, 581, 589, 597, 613, 629, 645 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Squarefree integers m for which the fundamental unit of Q(sqrt(m)) is of the form (u + v*sqrt(m))/2, where u and v are both odd. REFERENCES F. Arndt, Beiträge zur Theorie der quadratischen Formen, Archiv der Mathematik und Physik 15 (1850) 467-478. E. L. Ince, Cycles of Reduced Ideals in Quadratic Fields, British Association Mathematical Tables, Vol. IV, London, 1934. H. C. Williams, Eisenstein's problem and continued fractions, Utilitas Math. 37 (1990) 145-157. LINKS Robert G. Wilson v, Table of n, a(n) for n = 1..1000 (first 161 terms from Charles R Greathouse IV) A. Cayley, Note sur l'equation x^2 - D*y^2 = +-4, D=5 (mod 8), J. Reine Angew. Math. 53 (1857) 369-371. S. R. Finch, Class number theory Steven R. Finch, Class number theory [Cached copy, with permission of the author] Eric Weisstein's World of Mathematics, Fundamental unit MATHEMATICA fQ[n_] := Block[{nffu = NumberFieldFundamentalUnits@ Sqrt@ n}, SquareFreeQ@ n && Denominator[ nffu[[1, 2, 2]]] > 1]; Select[ 8Range@ 81 - 3, fQ] (* Robert G. Wilson v, Dec 22 2014 *) CROSSREFS Cf. A107998. Sequence in context: A004770 A191155 A107996 * A166095 A166090 A065766 Adjacent sequences:  A107994 A107995 A107996 * A107998 A107999 A108000 KEYWORD nonn AUTHOR Steven Finch, Jun 13 2005 STATUS approved

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Last modified June 20 09:12 EDT 2019. Contains 324234 sequences. (Running on oeis4.)