I don't know what I'd do without him

"I don't know what I'd do without him."Generally, Daniel feels he is progressing all the time towards "outgrowing" his autism. "If I heard somebody was sad I would picture myself sitting in the dark hollowness of number six to help me understand the feeling." Now his emotional life is more like everyone else's. "Love by its very nature puts things in perspective, joins the dots and helps me see life in a bigger way."Neil and Daniel, who have been together for six years, share an odd kind of domestic bliss. They have their tea together at exactly the same time every day; they have exactly 45g of porridge for breakfast, weighed on an electronic scale.

Emotions used to be difficult for him to understand without recourse to numbers. (He is a whizz at crowd-pleasers such as working out, from your date of birth, which day of the week you were born on.) "My parents had this phrase 'performing seal'. They didn't want me to be one."Growing up as an undiagnosed savant was never easy Daniel was lonely. "I was desperate for a friend and I used to lie in bed at night thinking about what it would be like.

My younger brothers and sisters had friends and I used to watch them playing to try to work out what they did and how friendship worked Then, I would have traded everything for normality. But I've since learned that being different isn't necessarily a bad thing."Falling in love with Neil has been a large part of this. But to him, it is more like an instinctive process: "Prime numbers feel smooth, like pebbles". The centre stays in close contact with Daniel."The scientists and researchers come to me so I can help them design the parameters of their experiments," he says in his habitual monotone, neither proud nor modest. It is important to Daniel that he uses his gifts responsibly, perhaps for science, perhaps for teaching: he is already devising a new system of visualisation to help with language learning and dyslexia."When I was growing up, my parents were very concerned that people shouldn't just get me to do tricks for them," he says. "My condition is invisible otherwise."Scientists at California's Center for Brain Studies were astounded when, two years ago, they discovered his facility for discerning prime numbers They had assumed he must have been trained to do it. He wasn't diagnosed with Asperger's syndrome until three years ago, at 25.

Sooner would have been better "both for me and my parents"; consciousness-raising is part of his motivation for writing his book. I never write anything down."His mathematical abilities are so extraordinary that it took a long time for them to be recognised. Daniel struggled at school (why, he wondered, were the numbers in the textbook not printed in their true colours, nine in blue, and so on?) He got a B at Maths GCSE. "Squaring numbers is a symmetrical process that I like very much," he says. "And when I divide one number by another, say, 13 divided by 97, I see a spiral rotating downwards in larger and larger loops that seem to warp and curve The shapes coalesce into the right number. While we were outside I noticed a spiral staircase in one of the buildings which was nice as it reminded me of doing a fraction in my head."Mental arithmetic is a gorgeous kaleidoscopic process for Daniel. I watch as he stands before The Independent on Sunday's photographer, as rigid as if he were in front of a firing squad.