%I
%S 0,0,0,1,1,1,1,2,4
%N First component x of pairs (x,y) where x <= y and x!+y! is a square, sorted on x.
%C Conjecture: the only solutions for x!+y!=n^2 (x <= y) are x=0,0,0,1,1,1,2,4 and y=4,5,7,4,5,7,2,5 respectively.
%o (PARI) sumfactsq(n) = { for(x=0,n, for(y=1,n, z = x!+y!; if(issquare(z),print1(x" ")) ) ) }
%Y Cf. A151819.
%K nonn
%O 1,8
%A _Cino Hilliard_, May 25 2003
%E Edited and corrected by _Farideh Firoozbakht_, Jul 07 2009
