Treasure values that go off the charts.

[Gluttony]

So the 'adding class levels' to a monster section of the Bestiary says that monsters with class levels get treasure equivalent to an NPC of their CR.

...What happens when a monster is at CR 20 or above? NPC levels don't go that high, and I'm not sure of what the math behind the NPC wealth chart is, so I have no idea how to advance the chart any further.

(In this particular instance, I need to figure out how wealthy a CR 25 dragon is supposed to be.)

[RDM42]

After jumping around a bit in the first seven levels of so, the WBL chart settles down into each new level being about 1.3 times the previous one.

[Chemlak]

At the high end, NPC wealth runs pretty close to 1.65 times per 2 levels. Extrapolating the chart at that rate:

21 = 203,000
22 = 263,000
23 = 335,000
24 = 434,000
25 = 553,000