Among the newbies in the Forbes list are four billionaires whose fortunes are tied to social networking site Facebook -- co-founders Dustin Moskovitz and Eduardo Saverin and investors Yuri Milner and Sean Parker. They join Facebook co-founder Mark Zuckerberg, who soared to No. 52 from No. 212 and now has an estimated worth of $13.5 billion, and Facebook investor Peter Thiel, who was also previously on the list. (Facebook billionaires: )

One of the biggest movers up the list was U.S. casino magnate Sheldon Adelson, who posted the biggest increase in wealth behind Slim.

He is worth $23.3 billion, up from $14 billion, and soared to No. 16 from No. 73 last year in a remarkable turnaround for a businessman whose Las Vegas Sands Corp came close to defaulting on its debt in 2008.

While India's number of billionaires did not increase much, their "average net worth ... is huge -- $4.5 billion for an Indian billionaire versus $2.5 billion for a Chinese billionaire," said Forbes.

Russia is also trumping China with 15 billionaires in the top 100, compared to China's one, while India has seven and Brazil three.

RICH AND GENEROUS

Microsoft co-founder Bill Gates held on to second place, growing his wealth to $56 billion from $53 billion last year, and investor Warren Buffett again came in third with $50 billion, up from $47 billion.

Buffett's Berkshire Hathaway Inc has fared better than Gates' Microsoft. Microsoft shares now trade about where they were a decade ago, while Berkshire shares have roughly doubled.

Forbes said that Gates would have still been the richest man in the world if he had not so far given $28 billion of his wealth to his foundation. He was only knocked off the top spot on the list twice between 1995 and 2010. (Gates philanthrophy: )

The wealth of the world's billionaires jumped 25 percent to $4.5 trillion and their average net worth rose to $3.7 billion from $3.5 billion. There were 47 people who dropped off the list, 42 who returned and 10 people who died. The number of women grew to 102 from 89 last year.

While positions have shifted, the top 20 was largely unchanged. New this year were Adelson, Russian steel baron Vladimir Lisin and David and Charles Koch, brothers behind an energy and manufacturing empire. They recently hit the headlines for their controversial support of conservative U.S. causes.