Finding the First 10-digit Prime in (a Billion) Digits of e (3 September 2017)
Back in 2004, Google ran a recruitment campaign where they posted the following billboard along the main freeway running through Silicon Valley, and later at other locations in the country:
For those who managed to find the answer, a second problem awaited on the secret web site, and those who solved that were then encouraged to send in a job application.
Effectively nerd sniped, I started playing with this problem sometime last year, and it led down a path to some excellent programming exercises.
This post describes a few different ways of solving the problem; from a Perl one-liner, to using hand-rolled fixed-point arithmetic (including an implementation of Improved division by invariant integers) or using binary splitting with GMP to compute a billion decimals of e.
Searching for "first 10-digit prime in e" quickly yields the answer: 7427466391 is the number we're looking for. But let's assume we found this problem early on, and that the solution had yet to be posted online. We can still benefit from the web by searching for "many digits of e". The first hit provides two million digits in which we can search for the solution, for example with a Perl one-liner:
