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%I #9 Nov 18 2015 05:58:41
%S 257,401,577,697,761,1009,1129,1297,1393,1489,1601,1897,2081,2153,
%T 2177,2329,2713,2777,2857,2993,3121,3137,3281,3889,4001
%N Exceptional odd numbers D that do not admit a solution to the Pell equation x^2 - D y^2 = +8 with both x and y odd.
%C These are the odd numbers 1 (mod 8), not a square, having in the composite case no prime factors 3 or 5 (mod 8), and the indefinite binary quadratic form x^2 - D*y^2 (with discriminant 4*D > 0) does not represent +8.
%C The odd numbers D which admit proper solutions to the Pell equation x^2 - D*y^2 = +8 with both x and y odd are given by A263012.
%Y Cf. A263011, A263012.
%K nonn
%O 1,1
%A _Wolfdieter Lang_, Nov 17 2015