### The Man Who Loved Only Numbers

Now that I'm voyaging again, I have many more opportunities to
read. Especially on this Port Davey trip, as the passengers are
nowhere near as much work as the school students. I've previously
mentioned my weakness for
pop-mathematics books, but I don't feel guilty reading a
biography. The
Man Who Loved Only Numbers is a biography of Paul Erdős, one of
the most prolific and strangest mathematicians who ever lived.

Paul had a lot of trouble operating in the real world, and the
book is at its best when retelling these stories. He had little
need for money, travelled the world with a couple of suitcases,
doing mathematics all the way, loved grapefruits but couldn't open
them, had his own language (children were called "epsilons", a
mathematician who retired was "dead" but a mathematician who died
had "left") and didn't see the problem with ringing people at
5:00am, because that's when they'd be home. He one turned up at a
colleague's door one Christmas Eve, and the first words out of his
mouth were "Merry Christmas. Let *f(n)* be the following
function...".

But even though his life was disconnected from the real world,
he had plenty of time for the people who lived in it. He had a
peculiar knack for matching mathematical problems to people, and
mentored a great many mathematicians during his travels. Needing
only a little money, he gave most of it to charities, beggars and
the homeless. He loved all children, regardless of their
mathematical talent, and cared for anyone he thought was
vulnerable. He was also an extremely principled man: in 1954 he was
invited to a conference in Amsterdam, but the US denied him a
re-entry permit. He resigned his university position and left the
country.

So here is an apparent contradiction: Erdős clearly lived apart
from the real world, but cared deeply about his fellow
mathematicians. I find his life hugely inspiring: he was able to
wander the world, working on mathematics and mathematicians,
getting along in his own peculiar way. The best part about his
story is that his family and friends made this life possible. It
would have been far too easy to write someone like him off as
crazy.

The book loses a little steam towards the end: the section on
Diophantine equations and Fermat's last theorem feels like it's
included just because.