.
So, the pairs of numbers in opposite sides are (1,6), (2,5), (3,4).
The number of pairs to check is so few ( only 3, actually ) that the quickest way is to multiply the numbers in pairs
and then compare, to get the ANSWER in this way, which is 12.
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Another way is to notice that the sum of numbers on opposite sides is always 7;
then to write the quadratic function q(n) = n*(7-n) and to find its maximum for integer values n from 1 to 6, inclusive.
If you want, you may go this way, but calculating three products and comparing the results is much faster.