How many trillionaires are there in the world?

There are 0, but due to inflation and I think you mean US dollars, each bill is getting more and more worthless as the years pass. However, here are COUNTRIES that amount to $1,000,000,000 and over(in order of wealth):

USA, Japan, China, Germany, UK, France, Russia, Italy, Brazil, Canada, India, Mexico, Australia, and South Korea. Those 14 countries are the ELITE of world economy. However, a better answer would have JAPAN as #1 because the US has a 13 trillion dollar debt(it is still growing). Even though it has a 14 trillion dollar economy, 14-13=1, so the USA technically has only a 1 trillion dollar economy, placing it next to S. Korea.

Listen man, that's not how it works. The external debt is not something that is substracted from the economy of a country, its like if you have 10 dollars and you owe someone 5. You still have 10 dollars, until you pay. The United States is in a pretty bad economic situation, how ever, it is by far, and will be for the next 30 years, the biggest economy in the world, there's no looking two ways at it.

In Vietnam there are at least 13 people worth more than trillion dong

In Korea there are 15 people worth more than trillion won http://www.forbes.com/lists/2010/83/Korea-rich-10_South-Koreas-40-Richest_Rank.HTML

Jajajaja, sorry to inform you the richest man in the world is Carlos Slim, lives in Mexico City and is worth 53 billion. Also, that Forbes page does not exist. What you should look at is the forbes list of Billionaires. The richest billionaire is worth 53 billion, a trillion is 1,000 billion.