From It's impossible to visit every planet in No Man's Sky. Year: 2014. Publisher: Polygon.
Sean Murray, co-founder of developing studio Hello Games, told IGN that the procedurally generated universe in No Man's Sky, the indie space exploration game that has captivated gamers since it was revealed in December, creates worlds on the scale of two to the power of 64.
In numerical terms, that's 18.4 quintillion planets, or 18,446,744,073,709,551,616 if you want to see all of the digits. Visiting that many planets in the game at the rate of 1 per second would take about, oh, 584 million years.
It seems most likely that the 18.4 quintillion number is referring to the possible "seed values" that can be used to generate a planet (at least according to this StackExchange answer ). So it's not a weird challenge. Just feed the seed into the planet generator, and out pops a planet.
However, the game itself is composed of multiple galaxies. When you...
visit the center of a galaxy
...you get teleported to a brand new galaxy, ready for exploration.
This makes me wonder how many planets exist per galaxy. If we go by the idea that the 18.4 quintillion number refer only to the possible RNG seeds, it is possible that these seeds could then be reused in the brand new galaxy, and thus there are actually more than 18.4 quintillion planets in the universe (and we can dismiss the Polygon's quote as mere hype). On the other hand, it's also equally likely that the possible RNG seeds are somehow dependent on the galaxy you're currently in...and that there really is only 18.4 quintillion planets in the universe...but if so, how many of these random seeds actually exist per galaxy?
I would strongly prefer any answers that contains proof, either from the game files or an official quote from the developers.