Talk:Shop/@comment-28556137-20160526032340/@comment-25856498-20160526111253

2^x means that the price of the cards doubles with each purchase. For example, from your equation, buying the 100th common would cost 2*(2^99) = 2^100 (due to x = 99) which is definitely 2 times itself 100 times in a row = 1 267 650 600 228 229 401 496 703 205 376 Gold, far more than a maximum of 1 million can buy.

The price increases linearly, and is no longer exponential.