# Where did the 18,446,744,073,709,551,616 number come from?

Reading about No Mans Sky, and hearing about the 18,446,744,073,709,551,616 planets there are, I’m curious, where did that number come from? Does that mean there are 18,446,744,073,709,551,616 unique planets, and if1 they’re all found, the next planet would be a repeat? Or does it mean they’ve places some kind of “hard limit” in the code for that number? Or something else completely?

My current guess, is they can calculate that their world generation algorithm has 18,446,744,073,709,551,616 unique output values, and any new planets after that would be repeats.

1 I know that this will never happen

Update: I’ve reached out to Hello Games, and if they reply (I imagine they’re still a little busy at the moment!) I’ll update this post with what they say.

18,446,744,073,709,551,616 is 2^64. I assume that this means the planet generation algorithm is based on a random seed that is a 64-bit number (e.g. the long type in many programming language). I don’t know how (or even if; how would anyone check?) they guarantee that all possible inputs are used and that none are repeated.

EDIT: While it’s still true that this number is 2^64 (and it still appears in some statements in the lore, so could be said to be the number of planets that exist in-universe), there are not this many planets in the game. Since the Atlas Rises update, there are 256 (257? It’s not entirely clear) galaxies, and each planet has a 12-digit hex coordinate that identifies it within the galaxy. This coordinate is divided into parts:

• 3 digits ea. X and Z coordinates of region (a region is a cube-shaped volume of space)
• 2 digits Y coordinate of region
• 3 digits system within region (known regions have 533 to 553 systems, so not all values are used)
• 1 digit planet within system (0 is not used, largest known system is 6 planets and 2 moons)

So, putting that all together, there are about 600 trillion systems. If eight bodies per system is typical (in practice this is a high estimate), that’s about 5 quadrillion, still far from the 18 quintillion being discussed here.

In practice it doesn’t matter, because if a new system were discovered every second, it would take 74,000 years to reach all of the systems in one galaxy.