To recap. On August 9, 2012, all of the following Dominion cards (excluding Dark Ages) share a particular quality. (None of the promo cards do.) Perhaps if you take a step back and look at all the cards together, the outlines of a solution will appear in your mind.
Don't worry about prime numbers and stuff like that. You don't need Google's calculator function to solve this; it's not that type of puzzle.
Quality 1:
Bank
Bridge
Chapel
City
Courtyard
Estate
Festival
Forge
Gold
Harvest
Inn
Laboratory
Pawn
University
Warehouse
EDIT: And village! Shoot.
And all these cards share a different quality, one that's (imprecisely) the opposite quality to Quality 1.
Quality 2:
Council Room
Noble Brigand
Walled Village
Worker's Village
Young Witch
OK, here's some more information.
The algorithm I run these cards through: I didn't design it.
Regarding Dark Ages. Of the previewed cards, only Rats has Quality 1. Ruined Market has Quality 2. Based on what I know of the unrevealed cards, I would guess that once they're all revealed, more cards will have Quality 2 than in any other set.
Also, I imagine that if someone slipped me a card list of the unpreviewed Dark Ages cards, and I ran them through the algorithm today, that ALMOST ALL of them would share Quality 1. Though I can't be sure. And of course, tomorrow will be a different story...
Oh yeah, third thing -- the results of this puzzle are very time sensitive. A year from now, all the answers could be different.
Good luck!