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EXAMPLE
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For n=2, the matrices are [0,0,0,0], [0,0,0,1], [0,0,0,2], [0,0,1,0], [0,0,1,1], [0,0,1,2], [0,0,2,0], [0,0,2,1], [0,0,2,2], [0,1,0,0], [0,1,0,1], [0,1,0,2], [0,1,1,0], [0,1,1,1], [0,1,1,2], [0,2,0,0], [0,2,0,1], [0,2,0,2], [1,0,0,0], [1,0,0,1], [1,0,1,0], [1,0,1,1], [1,0,2,0], [1,0,2,1], [1,1,0,0], [1,1,0,1], [1,1,1,0], [1,2,0,0], [1,2,0,1], [2,0,0,0], [2,0,1,0], [2,0,2,0], [2,1,0,0], [2,1,1,0], [2,2,0,0].
Here each of these matrices M is defined as M=[a,b,c,d], where a=M[1][1], b=M[1][2], c=M[2][1], d=M[2][2]. There are 35 possibilities. So for n=2, a(n)=35.
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