Most of us in the mathematics profession know at least the basic outline of Paul Erdős’s life: brilliant, Hungarian, prodigy, peripatetic mathematician who spent a lifetime fostering collaborations all around the world, engendering the concept of an Erdős number.

Before reading the book I wondered how Heiligman and Pham would make a successful children’s book of Erdős’s singular, eccentric life. Several years ago I had read the popular Erdős biography by Paul Hoffman (*The* *Man Who Loved Only Numbers)*, and the one worry I carried away from that delightful book was that it might inadvertently reinforce the stereotype that many in the general public have about mathematicians — that we must be a bit weird to love such an abstruse discipline.

Given this concern going in, I was happy that *The** Boy Who Loved Math *left me with no such worries. First, I realized that children are — thankfully — not yet imbued with the notion that “different = weird.” When I read the book to my grandson (age 4½) I could see that the book engaged him as a story: he could relate to it, and it entertained him.

Heiligman chooses a theme that works well with children: aversion to rules. Much of children’s literature uses this theme to great advantage. *Tom Sawyer* is a classic example. Tom was both accomplished and assiduous in his avoidance of rules, but his passion was so deep that he “apprenticed” with his wayward buddy Huck in order to elevate his game a couple of notches.

“Paul hated rules” recurs through the story. The first rules enforcer is the family nanny Fräulein, whose earnestness is conveyed beautifully through Pham’s drawings. Then Paul encounters the rules of elementary school, familiar rules such as sitting in one’s desk. Finally, we get to Erdős’s unusual adult life-style. “And he still didn’t like to follow rules. So he invented his own way to live” is how Heiligman puts it. Because most children understand a child wanting to break rules (at least sometimes) it seems natural that maybe an adult can afford to do the same. And so, the adult Paul is made to seem less weird or eccentric.

When the weirdness is taken away, we are left with the story of a boy who is both different and has a passion that he follows through his entire life. Since most of us, beginning in our childhood, often feel out of step with at least some aspects of society, I would view *The Boy Who Loved Math *as an affirmation that being different is okay. And since many of us as children may find ourselves passionate about something, it is nice to have affirmation that it is right to follow that passion.

I don’t mean to suggest that the primary purpose of literature — including children’s literature — should be didactic, but to the extent that some lessons are inevitably going to be “taught” by a biography, I would prefer they be the right lessons.

One message this book definitely brings home is that numbers are way cool. The book swims with numbers: numbers of seconds in a lifetime, prime numbers, negative numbers, Erdős numbers, and even what I’ll call bonus numbers. For example in sentences such as “Even Fräulein was better than school. Maybe 500 times better,” the 500 is a bonus, one the author could easily have avoided. The book abounds in bonus numbers, almost always rendered in numerals, rather than words.

Pham incorporates numbers and other mathematical objects into almost every page of the book in beautiful and clever ways. There are numerals embedded into the architecture of Budapest, a picture of Paul the boy playing with the Sieve of Eratosthenes, combinatorial identities, famous graphs, tilings, and so on.

One novel feature of the book is the two sets of endnotes written by Heiligman and Pham. Neither of them is a mathematician, but both worked hard to get the mathematics right, and these notes should be interesting to the adult reading the book or to an older child with a budding interest in mathematics.

As I read the book to my grandson, he grinned with each appearance of Fräulein and each instance of Paul not liking rules. And that night, when he drew the symbol for infinity in the air for his father and told him it was like a figure 8, I saw that he’d picked up some of the mathematics as well. While my 4-year-old enjoyed the book, I feel he is at the young end of the spectrum the book would appeal to, because it is rich enough in mathematical ideas and engaging enough as a beautifully illustrated story to appeal to much older children as well. I highly recommend it.

Tom Moore is a professor of mathematics and statistics at Grinnell College, where he has been since 1980. His main interest has been in statistics education, but during his time he has taught a variety of mathematics courses as well, including combinatorics, his closest brush with the mathematics of Paul Erdős. While his Erdős number appears to be 4, his Erdős dinner number is definitely 1.