I explained in a previous post what the following relates to. Check it out if you're confused.
Savant Syndrome Fact 4:
To savants who experience synesthesia, numbers can vary in their "degree of beauty." To Daniel Tammet, an extremely high-functioning or "prodigious" savant, a telephone number with the sequence 189 is much more beautiful than one with the sequence 116. A good comparison would be how, just as it would be impossible for a hearing person to explain to a deaf individual why the sounds of a chainsaw or nails on a chalkboard are horrible and grating noises, it is impossible for Tammet to explain to others why one number is more beautiful than another. It is as though he has an additional mental sense that most people lack. Not all savants experience numbers as having shapes, patterns, or varying levels of beauty.