This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A068716 #15 Aug 29 2020 10:47:09 %S A068716 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 A068716 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 A068716 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 A068716 a(n) = 1 if x^2 + 1 = n * y^2 has infinitely many solutions in integers (x,y), otherwise a(n) = 0. %D A068716 H. Davenport, The Higher Arithmetic. Cambridge Univ. Press, 7th ed., 1999, table 1. %H A068716 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 A068716 a(n) = 1 - (A067280(n) mod 2 ). %e A068716 a(2) = 1 as x*x + 1 = 2 * y*y is soluble, e.g., 7*7 + 1= 2*5*5. %Y A068716 Cf. A068717, A067280, A006702, A006703. %K A068716 nonn %O A068716 1,1 %A A068716 _Frank Ellermann_, Feb 25 2002 %E A068716 More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 31 2003