BULLIED by other children and bewildered by ordinary life, Daniel Tammet spent his early years burrowed deep inside the world of numbers. They were his companions and his solace, living, breathing beings that enveloped him with their shapes and textures and colors.
He still loves them and needs them; he can still do extraordinary things with them, like perform complicated calculations instantly in his head, far beyond the capacity of an ordinary calculator. But Mr. Tammet, who at the age of 25 received a diagnosis of Asperger's syndrome, a high-functioning form of autism, has made a difficult and self-conscious journey out from his own mind.
''I live in two countries, one of the mind and one of the body, one of numbers and one of people,'' he said recently. Slight and soft-spoken, dressed in a T-shirt and casual combat-style pants, he sat cross-legged in his living room and sipped a cup of tea, one of several he drinks at set times each day.
Not so long ago, even a conversation like this one would have been prohibitively difficult for Mr. Tammet, now 28. As he describes in his newly published memoir, ''Born on a Blue Day: Inside the Extraordinary Mind of an Autistic Savant'' (Free Press), he has willed himself to learn what to do. Offer a visitor a drink; look her in the eye; don't stand in someone else's space. These are all conscious decisions.
Recently, some friends warned him that in his eagerness to make eye contact, he tended to stare too intently. ''It's like being on a tightrope,'' he said. ''If you try too hard, you'll come off. But you have to try.''
Mr. Tammet's house, a small cottage in a sleepy cul-de-sac in this quiet Kent town, is a refuge from the sensory assaults of the world outside -- the city, big supermarkets, crowds -- which tend to overwhelm and unnerve him.
''The house is like my oasis,'' he said. ''I structured it -- the colors of it, the way the furniture is laid out. The way it feels, and the way I work -- it's very much a matter of routine, and it makes me feel calm and comfortable.''
Mr. Tammet's book is an elegant account of how his condition has informed his life, a rare first-person insight into a mysterious and confounding disorder. He is unusual not just because of his lucid writing style and his ability to analyze his own thoughts and behavior, but also because he is one fewer than 100 ''prodigious savants'' -- autistic or otherwise mentally impaired people with spectacular, almost preternatural skills -- in the world, according to Dr. Darold Treffert, a researcher of savant syndrome.
He wears his gifts lightly, casually. When he gets nervous, he said, he sometimes reverts to a coping strategy he employed as a child: he multiplies two over and over again, each result emitting in his head bright silvery sparks until he is enveloped by fireworks of them. He demonstrated, reciting the numbers to himself, and in a moment had reached 1,048,576 -- 2 to the 20th power. He speaks 10 languages, including Lithuanian, Icelandic and Esperanto, and has invented his own language, Mantï. In 2004, he raised money for an epilepsy charity by memorizing and publicly reciting the number pi to 22,514 digits -- a new European record. In addition to Asperger's, he has the rare gift of synesthesia, which allows him to see numbers as having shapes, colors and textures; he also assigns them personalities. His unusual mind has been studied repeatedly by researchers in Britain and the United States.
Mr. Tammet sees himself as an ambassador and advocate for people with autism.
''Autistic people do fall in love,'' he said. ''They do have joy; they do have sorrow; they do experience ups and downs like everyone else. We may not have the same ability to manage those emotions as others have, but they're there, and sometimes our experience of them is far more intense than the experience of other people.''
Mr. Tammet grew up in east London, one of nine children. He suffered a series of early epileptic fits that he believes brought on his synesthesia. Through his childhood troubles -- a lack of friends, the tendency to block out the world, an incessant counting of everything countable -- he was buoyed by a loving family whose size ensured, he said, that ''I could never close inside myself.''