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A082871 First component x of pairs (x,y) where x <= y and x!+y! is a square, sorted on x. 1

%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

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Last modified July 11 23:43 EDT 2020. Contains 335653 sequences. (Running on oeis4.)