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A156381
Number of 3 X 3 arrays of squares of integers, symmetric about both diagonal and antidiagonal, with all rows summing to n.
0
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, 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, 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
OFFSET
0,2
COMMENTS
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
EXAMPLE
All solutions for n=9
...0.0.9...1.4.4...4.4.1...9.0.0
...0.9.0...4.1.4...4.1.4...0.9.0
...9.0.0...4.4.1...1.4.4...0.0.9
CROSSREFS
Cf. A002479.
Sequence in context: A129402 A128580 A104405 * A089077 A203398 A339275
KEYWORD
nonn
AUTHOR
R. H. Hardin Feb 09 2009
STATUS
approved