For as long as I can remember, I have experienced numbers in the visual, synesthetic way that I do. Numbers are my first language, one I often think and feel in. Emotions can be hard for me to understand or know how to react to, so I often use numbers to help me. If a friend says they feel sad or depressed, I picture myself sitting in the dark hollowness of number 6 to help me experience the same sort of feeling and understand it. If I read in an article that a person felt intimidated by something, I imagine myself standing next to the number 9. Whenever someone describes visiting a beautiful place, I recall my numerical landscapes and how happy they make me feel inside. By doing this, numbers actually help me get closer to understanding other people.
Sometimes people I meet for the first time remind me of a particular number and this helps me to be comfortable around them. They might be very tall and remind me of the number 9, or round and remind me of the number 3. If I feel unhappy or anxious or in a situation I have no previous experience of (when I'm much more likely to feel stressed and uncomfortable), I count to myself. When I count, the numbers form pictures and patterns in my mind that are consistent and reassuring to me. Then I can relax and interact with whatever situation I'm in.
Thinking of calendars always makes me feel good, all those numbers and patterns in one place. Different days of the week elicit different colors and emotions in my head: Tuesdays are a warm color while Thursdays are fuzzy. Calendrical calculation -- the ability to tell what day of the week a particular date fell or will fall on -- is common to many savants. I think this is probably due to the fact that the numbers in calendars are predictable and form patterns between the different days and months. For example, the thirteenth day in a month is always two days before whatever day the first falls on, excepting leap years, while several of the months mimic the behavior of others, like January and October, September and December, and February and March (the first day of February is the same as the first day of March). So if the first of February is a fuzzy texture in my mind (Thursday) for a given year, the thirteenth of March will be a warm color (Tuesday).
In his book The Man Who Mistook His Wife for a Hat, writer and neurologist Oliver Sacks mentions the case of severely autistic twins John and Michael as an example of how far some savants are able to take calendrical calculations. Though unable to care for themselves (they had been in various institutions since the age of seven), the twins were capable of calculating the day of the week for any date over a 40,000-year span.
Sacks also describes John and Michael as playing a game that involved swapping prime numbers with each other for hours at a time. Like the twins, I have always been fascinated by prime numbers. I see each prime as a smooth-textured shape, distinct from composite numbers (non-primes) that are grittier and less distinctive. Whenever I identify a number as prime, I get a rush of feeling in my head (in the front center) which is hard to put into words. It's a special feeling, like the sudden sensation of pins and needles.