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 A068716 a(n) = 1 if x^2 + 1 = n * y^2 has infinitely many solutions in integers (x,y), otherwise a(n) = 0. 2
 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES H. Davenport, The Higher Arithmetic. Cambridge Univ. Press, 7th ed., 1999, table 1. LINKS John Robertson, Solving the generalized Pell equation x^2-dy^2=N. FORMULA a(n) = 1 - (A067280(n) mod 2 ). EXAMPLE a(2) = 1 as x*x + 1 = 2 * y*y is soluble, e.g., 7*7 + 1= 2*5*5. CROSSREFS Cf. A068717, A067280, A006702, A006703. Sequence in context: A033684 A080885 A258998 * A188020 A179828 A129184 Adjacent sequences:  A068713 A068714 A068715 * A068717 A068718 A068719 KEYWORD nonn AUTHOR Frank Ellermann, Feb 25 2002 EXTENSIONS More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 31 2003 STATUS approved

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Last modified June 13 15:33 EDT 2021. Contains 345008 sequences. (Running on oeis4.)