The current configuration of URL's for memes on Imgflip is like the odometer on a car, always goes up with each new meme.
imgflip.com/i/222222
is higher (and newer) than
imgflip.com/i/200000
If you download the image from that second URL, the file will be named 200000.jpg
Because the Imgflip URL configuration uses numbers and letters, there are 36 possibilities for a position in the alphanumeric image name.
There are 5^36 possible URLs between
imgflip.com/i/400000
and the next possible rollover meme
imgflip.com/i/500000
(coming in the future, check back in about a year)