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The top number will always be 12+8x,where "x" is the number entered in the lowest left corner.

Conversely,the number entered can be determined by x=(y-12)/8

Also the number at the top is the twice the sum of the digits at the bottom row.

Also the number at the top is the sum of the 2nd row from the bottom and the 2nd element of that row.

The 12 in the formula came because of 2*(0+1+2+3)=12.

The number at the top will always be a multiple of 4 because both 12 and 8x are multiples of 4.

The first element of the top 2nd row is 4+4x.
The second element of the top 2nd row is (4+4x)+4