This will be a very technical post, but I wanted to note this somewhere (and even make it useful for others!). Still, even if you're no command line whiz-kid but you're curious in the answer I got, skip to the end!
Let's start at the beginning. What is Google's IP address, you might have wondered at some point. Domain names are ways of referring you to an IP address, so google.com must lead you to one, right? Well yes, except it leads you to many. Each time you go to google.com, your computer looks up its IP address and it often gets a different answer each time. Google has so much traffic that it has many IP addresses for its servers, and gives you the address of the closest (or least busy) one whenever you ask.
So how many does it have in total, and what are they? Well, you can try asking a bunch of times and writing them down. I actually wrote a wrote a script to do that, before I realized maybe I should, say, Google for an answer. (To be fair, I'd done that before but came up short.) What I found was a page from Google's own help documents titled "Google IP address ranges." This page points out a useful trick: SPF records.