Sometimes I close my eyes and imagine the first thirty, fifty, hundred numbers as I experience them spatially, synesthetically. Then I can see in my mind's eye just how beautiful and special the primes are by the way they stand out so sharply from the other number shapes. It's exactly for this reason that I look and look and look at them; each one is so different from the one before and the one after. Their loneliness among the other numbers makes them so conspicuous and interesting to me.
There are moments, as I'm falling into sleep at night, that my mind fills suddenly with bright light and all I can see are numbers -- hundreds, thousands of them -- swimming rapidly over my eyes. The experience is beautiful and soothing to me. Some nights, when I'm having difficulty falling asleep, I imagine myself walking around my numerical landscapes. Then I feel safe and happy. I never feel lost, because the prime number shapes act as signposts.
Mathematicians, too, spend a lot of time thinking about prime numbers, in part because there is no quick or simple method for testing a number to see whether or not it is prime. The best known is called "the Sieve of Eratosthenes" after an ancient Greek scholar, Eratosthenes of Cyrene. The sieve method works in this way: Write out the numbers you want to test, for example 1 to 100. Starting with 2 (1 is neither prime nor composite), cross out every second number: 4, 6, 8...up to 100. Then move to 3 and cross out every third number: 6, 9, 12...then move to four and cross out every fourth number: 8, 12, 16...and so on, until you are left with only a few numbers that do not ever get crossed out: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31...These are the prime numbers; the building blocks of my numerical world.
My synesthesia also affects how I perceive words and language. The word ladder, for example, is blue and shiny, while hoop is a soft, white word. The same thing happens when I read words in other languages: jardin, the French word for "garden," is a blurred yellow, while hnugginn -- Icelandic for "sad" -- is white with lots of blue specks. Synesthesia researchers have reported that colored words tend to obtain their colors from the initial letter of the word, and this is generally true for me: yogurt is a yellow word, video is purple (perhaps linked with violet) and gate is green. I can even make the color of a word change by mentally adding initial letters to turn the word into another: at is a red word, but add the letter H to get hat and it becomes a white word. If I then add a letter T to make that, the word's color is now orange. Not all words fit the initial-letter pattern: words beginning with the letter A, for example, are always red and those beginning with W are always dark blue.
Some words are perfect fits for the things they describe. A raspberry is both a red word and a red fruit, while grass and glass are both green words that describe green things. Words beginning with the letter T are always orange like a tulip or a tiger or a tree in autumn, when the leaves turn to orange.
Conversely, some words do not seem to me to fit the things they describe: geese is a green word but describes white birds (heese would seem a better choice to me), the word white is blue while orange is clear and shiny like ice. Four is a blue word but a pointy number, at least to me. The color of wine (a blue word) is better described by the French word vin, which is purple.