%I #15 Aug 29 2020 10:47:09
%S 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,
%T 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,
%U 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
%N a(n) = 1 if x^2 + 1 = n * y^2 has infinitely many solutions in integers (x,y), otherwise a(n) = 0.
%D H. Davenport, The Higher Arithmetic. Cambridge Univ. Press, 7th ed., 1999, table 1.
%H John Robertson, <a href="https://web.archive.org/web/20051102095831/http://hometown.aol.com/jpr2718/pell.pdf">Solving the generalized Pell equation x^2-dy^2=N</a>.
%F a(n) = 1 - (A067280(n) mod 2 ).
%e a(2) = 1 as x*x + 1 = 2 * y*y is soluble, e.g., 7*7 + 1= 2*5*5.
%Y Cf. A068717, A067280, A006702, A006703.
%K nonn
%O 1,1
%A _Frank Ellermann_, Feb 25 2002
%E More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 31 2003