Amir D. Aczel, 65, a mathematician who launched a second career as a best-selling author, most notably of Fermat's Last Theorem, about how an enduring enigma of mathematics was ultimately solved, died Nov. 26 in Nimes, France. The cause was cancer, said his wife, Debra Gross Aczel.

Mr. Aczel spent years as a professor in Alaska and Massachusetts and wrote textbooks on math and statistics before discovering a talent for explaining the world of science and numbers to ordinary readers. He first gained widespread acclaim in 1996 with Fermat's Last Theorem: Unlocking the Secret of an Ancient Mathematical Problem.

The problem had been one of the great unsolved mysteries of mathematics since about 1637, when a French jurist and amateur mathematician named Pierre de Fermat wrote an equation in the margin of a book, followed by the tantalizing words: "I have discovered a truly marvelous proof of this, which, however, the margin is not large enough to contain."

In his book, Mr. Aczel fashioned a page-turning thriller of intellectual adventure that, in his words, "spans mathematical history from the dawn of civilization to our own time." It wasn't until the 1990s that Andrew Wiles, a British mathematician at Princeton University, finally unlocked the mystery.

Mr. Aczel's 147-page book was "a captivating volume," New York Times critic Richard Bernstein wrote, "rooted in the pleasure of pure knowledge."

It spent months on best-seller lists and made Mr. Aczel something of an all-purpose explicator of scientific and mathematical phenomena.

- Washington Post