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A156381 Number of 3X3 arrays of squares of integers, symmetric about both diagonal and antidiagonal, with all rows summing to n. 0

%I

%S 1,2,2,1,2,0,2,0,2,4,0,2,1,0,0,0,2,2,4,2,0,0,2,0,2,4,0,3,0,0,0,0,2,4,

%T 4,0,4,0,2,0,0,4,0,2,2,0,0,0,1,2,4,5,0,0,4,0,0,4,0,2,0,0,0,0,2,0,6,2,

%U 2,0,0,0,4,2,0,3,2,0,0,0,0,8,2,2,0,0,2,0,2,4,0,0,0,0,0,0,2,2,2,7,4,0,4,0,0,0,0,2

%N Number of 3X3 arrays of squares of integers, symmetric about both diagonal and antidiagonal, with all rows summing to n.

%C a(n) is nonzero if and only if n = x^2 + 2*y^2 for some integers x and y if and only if n is in A002479. - _Michael Somos_, Dec 15 2011

%e All solutions for n=9

%e ...0.0.9...1.4.4...4.4.1...9.0.0

%e ...0.9.0...4.1.4...4.1.4...0.9.0

%e ...9.0.0...4.4.1...1.4.4...0.0.9

%Y Cf. A002479.

%K nonn

%O 0,2

%A _R. H. Hardin_ Feb 09 2009

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Last modified January 25 07:44 EST 2020. Contains 331241 sequences. (Running on oeis4.)