Trivia

No location permits were secured for any of the scenes filmed. The crew had to have one man constantly serving as a lookout for police so they could stop filming if needed.
Pi cost only \$60,000 to make, most of which was raised in the form of individual \$100 contributions from the director's friends and family. When it was later bought by Artisan Entertainment, each contributor got back a \$150 return on their investment.
The 216-digit number which Max hand-writes on paper (different from the 218-digit number displayed on-screen by Euclid) is: 884509627386359275033751967 943067599621731590401694134 434007629683591574337516791 197615733475195375920401694 343151239621353184932676605 800621596380716399501371459 954387507655892533875618750 354029981152863950711207613. The piece of paper he writes it on has "Only God is Perfect" at the bottom.
Max suggests that the Kabbalists have already tried all possible 216-digit numbers. That is 10 to the power of 215 multiplied by 9. [9x(10^215)] The result is a number length of 216 decimal digits. The number of atoms in the visible universe is only 80 digits, so it is obviously impossible for them to have tried them all.
The number written in the opening sequence of the film is not Pi beyond the first 8 decimals.
Darren Aronofsky's mother catered for the film.
Backstories for the characters Max and Sol were conceived by Sean Gullette and Darren Aronofsky, but never written for the film. They included: Max was proved to be a math prodigy very young, and soon attended Columbia University, where he met Sol, an Russian expatriate, who was captured by American Forces and was given the chance to assist in the building of nuclear weapons because of his great math prowess, he refused, and was relocated to Siberia, where he was soon let out, and got a job teaching math at Columbia University. If you look closely at Sol's wrists, you can see prison tattoos.
The number Max is searching for is 216 digits long. 216 is 6x6x6; 666 is the "number of the beast" according to the Book of Revelation.
Bought by Artisan for \$1,000,000.
Darren Aronofsky's feature debut.
Most of the props on the set were hot-glued together. That, plus the hot lights and the cramped quarters created by the sets, caused a number of crewmembers to grow nauseous from the smell.

Spoilers

The trivia item below may give away important plot points.

The movie ends with Jenna asking for the result of the division of 748 by 238. This simplifies to the fraction 22/7, the result is 3.1428 which is a good approximation of pi often taught in primary schools. (3.1415...) by 3 digits.