There are only 19 countries in the G-20

and Jim Vreeland teaches you how to remember them: G7 + EU + BRIC + MAKITSAS.

(The twentieth member is ... the European Union. I think this is unfair, since the Euro-members of the G-7 are thereby getting two bites at the apple. I demand that California and Texas get representation as well, similar to how Ukraine and Belarus had UN seats even when they were Soviet satellites.)