Big Oh time complexity for alpha(n)

Question

What does O(alpha(n)) mean? I recently stumbled upon 2048 but in terms of run times and one of the blocks had that. Thanks!

Answer 1

It appears to be a reference to the inverse Ackermann function, written as α(n)

From wikipedia:

This inverse appears in the time complexity of some algorithms, such as the disjoint-set data structure and Chazelle's algorithm for minimum spanning trees.