The Grapes of Math
CHAPTER ONE
Every Number Tells a Story
Jerry Newport asked me to pick a four-digit number.
"2761," I said.
"That's 11 x 251," he replied, reciting the numbers in one continuous, unhesitant flow.
"2762. That's 2 x 1381.
"2763. That's 3 x 3 x 307.
"2764. That's 2 x 2 x 691."
Jerry is a retired taxi driver from Tucson, Arizona, with Asperger's syndrome. He has a ruddy complexion and small blue eyes, his large forehead sliced by a diagonal comb of dark blond hair. He likes birds as well as numbers, and when we met he was wearing a flowery red shirt with a parrot on it. We were sitting in his living room, together with a cockatoo, a dove, three parakeets and two cockatiels, which were also listening to, and occasionally repeating, our conversation.
As soon as Jerry sees a big number, he divides it up into prime numbers, which are those numbers—2, 3, 5, 7, 11 . . .—that can be divided only by themselves and 1. This habit made his former job driving cabs particularly enjoyable, since there was always a number on the license plate in front of him. When he lived in Santa Monica, where license numbers were four and five digits long, he would often visit the four-story car park of his local mall and not leave until he had worked through every plate.
In Tucson, however, car numbers are only three digits long. He barely glances at them now.
"If the number is more than four digits I'll start to pay attention to it. If it's four digits or less, it's roadkill. It is!" he remonstrated. "Come on! Show me something new!"
Asperger's is a psychological disorder in which social awkwardness
can coexist with extreme abilities, such as, in Jerry's case, an extraordinary talent for mental arithmetic. In 2010 he competed at the Mental Calculation World Cup in Germany having done no preparation. He won the overall title of Most Versatile Calculator, the only contestant to score full marks in the category where 19 five-digit numbers have to be decomposed into their constituent primes in ten minutes. No one else got even close.
Jerry's system for breaking down large numbers is to sieve out the prime numbers in ascending order, extracting a 2 if the number is even, extracting a 3 if it divides by three, a 5 if it divides by five, and so on.
He raised his voice to a yell: "Oh yeah, we're sievin', baby!" He started moving his body around: "We're onstage. Throw those numbers out, crowd, and we'll sieve 'em for ya! Yeah! Jerry and the Sievers!"
"I've got a pair of sievers," interrupted his wife, Mary, who was sitting on the sofa next to us. Mary, a musician and former Star Trek extra, also has Asperger's, which is much less common in women than it is in men. A marriage between two people with Asperger's is very rare, and their unconventional romance was turned into the 2005 Hollywood movie Mozart and the Whale.
Sometimes Jerry cannot extract any primes at all from a large number, which means the number is itself prime. When this happens it gives him a thrill: "If it's a prime number I've never found before, it's kinda like if you were looking for rocks, and you've found a new rock. Something like a diamond you can take home and put on your shelf."
He paused. "A new prime number—it's like having a new friend."