I don’t know what a synesthete is, but 9 is also my favorite. It’s easy to write, numerically or as a word (gentle curves), and you can write it two ways, starting at the top of the loop or at the inside.
My least favorites are two and eight – the words have no visual relationship to the numerals. I can’t explain why, but I can associate the other number words with their numerals – they “match”, at least in my head.
19 is significant in my life, and I was tickled when I got a new cell phone and was assigned a number that added up to 19 – 2566.
Speaking of 666: the indoor temperature thingie read 66 (degrees) and 66 (humidity) yesterday. I waited for the sky to fall but it didn’t.
My favorite by far is 0. Everything’s easier when zero’s involved. Anything plus zero? No problem, that’s just the same thing again. Anything minus zero? Ditto. Anything times zero? Easy, that’s just zero. Zero to any power? Zero. Anything to the zero power? That’s easy, too, one. Anything divided by zero? Also easy: I know it’s impossible, no matter what I started with.
My favorite number is probably three, because the third time is when something has to happen, as with a joke, and if it doesn’t, you can stop listening. The exception, I guess, is the “orange you glad I didn’t say banana again?” joke, but I can make an exception for that. Also in a song, you get the bridge after the second verse, and that keeps you awake through the rest of the song.
As for Arabic numerals, I would rank them roughly 2,4 and 7, then 3,6,9 and 0, then 1,8 and 5, though my taste is not constant.
I somehow knew I wouldn’t be the only 47 fancier. I just started noticing it everywhere one day and I’ve grown to like it. I used to wear a necklace with 47 on it, even.