Find easter on any given year
The usual advice is "make meaningful variables". However, we know this algorithm (essentially a modification of that published by a young Gauß) and those variables don't have a simple meaning. (See Decoding Gauss Easter algorithm). We know b represents centuries, but even if you did find a word to describe what the variables represent, would using epact or even ageOfMoonOnJanFirst help to understand the algorithm? The variable represent stages of the algorithm. As Gauss wrote "It is not possible to present the full analysis that led to the algorithm".

So the usual cure of incomprehensible code - clear variables names - won't help much here.  What can we do for the poor person who has to maintain this code 6 months, or 6 years, later?  We can let them know where this algorithm comes from. This is easy enough. A comment referencing the source would allow someone seeing this to check that it is still doing what it is supposed to do.

Beyond adding this comment, the algorithm for calculating Easter is unlikely to be a bottleneck in any piece of software, so assuming that this algorithm is correct (proven and tested) I would leave it as is.