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A064276
Number of 2 X 2 singular integer matrices with elements from {0,...,n} up to row and column permutation.
2
1, 5, 13, 25, 42, 62, 90, 118, 155, 195, 243, 287, 352, 404, 472, 548, 629, 697, 797, 873, 986, 1094, 1202, 1294, 1443, 1559, 1687, 1823, 1984, 2100, 2296, 2420, 2597, 2769, 2937, 3125, 3366, 3514, 3702, 3906, 4167, 4331, 4611, 4783, 5040, 5320, 5548
OFFSET
0,2
FORMULA
a(n) = (A059306(n)+(n+1)*(2*n+3))/4.
EXAMPLE
There are 5 binary singular matrices up to row and column permutation:
[0 0] [1 0] [1 1] [1 0] [1 1]
[0 0] [0 0] [0 0] [1 0] [1 1].
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladeta Jovovic, Sep 24 2001
EXTENSIONS
More terms from David Wasserman, Jul 16 2002
STATUS
approved