No, it's not that unusual. Or perhaps it is. But then, numbers for me are dots on a meandering line. One to ten go straight up, eleven to twenty then go to the right, 21 goes a step down and further to the right, from 30 onward everything goes straight up. It's easy for me to remember numbers (phone numbers, prices, the like) because I know where the number was; it does not help at all when trying to do maths, which I therefore rarely attempt if I can help it.

Colour-sorted bookshelves exist, too -- see here.