Arithmetician = Advanced Arcanist?

[Rongway]

How has Aritmetician functioned previously? It doesn’t sound like a battle class to me.

Prior to Tactics, there were monster attacks such as "Level 5 Death", which would kill anyone whose level was divisible by 5; these appear in XIV in the Agra Manyu fight in World of Darkness as "Lv150 Death" (kills everyone inside the circle if the total levels are divisible by 150 (in practice, a multiple of 3 people inside the circle)) and "Lv100 Flare" (major damage to everyone if levels total a multiple of 100).

In Tactics, the playable job Calculator (later renamed Arithmetician) was implemented with its abilities fitting into two groups: a parameter selection (CT (a sort of "initiative"), Level, EXP, Height (of the terrain)) and a target set of numbers (Prime, Multiples of 3, ...4, ...5). After selecting one ability from each group, anyone whose [selected parameter] was in the chosen number set would take magic damage. So if all your party were levels not-multiples-of-3 but the enemy party had several people whose levels were multiples of 3, your Arithmetician might choose Level Multiples of 3. Or if your party were all standing on terrain tiles of height 1 but the enemies were on terrain tiles of height 2, you could use Height Prime.

The math boss in XIV is basically doing a variation of "HP Prime" / "HP Multiples of x" in which instead of doing damage to everyone who meets the criterion, it rewards those people and punishes everyone who does not.