Pentation

Pentation is the 5th hyperoperation, and the first one is addition. Pentation is just repeated tetration, but it produces
extremely large unimaginable numbers, a simple 2 ↑↑↑ 3 (or often displayed as 32) is equal to 65,536.
Another example is 3 ↑↑↑ 2. It is equal to 7,625,597,484,987 (~7.625 trillion)

Pentation is calculated like this:
2 ↑↑↑ 3 = 2²2 = ⁴2 = 2^2^2^2 = 65,536

 Etymology 
The word "Pentation" was coined by Reuben Goodstein (An English Mathematician) by joining together penta- (which means five) and iteration (A mathematical
function). It's how he usually named hyperoperations.

 References 

Category:Hyperoperations