Graham's number
One can think of  as  because two arrows between numbers A and B just means A written down a B number of times with an arrow in between each A. Because we know what single arrows are,  is 3 multiplied by itself  times and we know  is twenty-seven. So  is 3x3x3x3x....x3x3, in total 27 times. That equals 7,625,597,484,987.