I have noticed, by chance, but I would very easily remember a phone number, if it has some digits symmetry, e.g. "540 045" (and mind you, I have very hard time memorizing numbers in general). At the same time, I have noticed that commercial companies would you use special phone numbers, using digits repetition, e.g. "67 67 67", in order to make them easier to memorize - but I can't say I would memorize a phone number in that format easier than in the "symmetrical format".
(I acknowledge though, that the "repetition format" is still better than any other format with no particular pattern.)
Therefore, my question is: is it universally valid among people that "symmetrical formats" are the easiest to memorize and if so, what could be the explanation?