“This question was first officially “answered” in 1974, and LEGO mathematicians arrived at the number 102,981,500. Eilers was curious about the mathematical methodology behind that number, and soon discovered that it only covered one kind of stacking—thus, it was dramatically low. So he wrote a computer program that modeled all the possible brick combinations. After running the program for a week, he ended up with a massive number: 915,103,765 combinations.” mentalfloss.com
The times involved by adding bricks seem to get into ranges we read about in articles about the times it takes to crack passwords.