Born into a poor Jewish family in Romania in 1931, Mandel developed a passion for mathematics at a young age but could not pursue an academic career because of financial hardship. Instead, he worked as an accountant to support his family.

His monthly salary of $88 was barely enough to support his family. Mandel told NPR's Planet Money in a 2016 interview that he needed a way to "get some serious money, quickly."

Having spent years studying probability theory and the work of Italian mathematician Leonardo Fibonacci, he began exploring the lottery, convinced mathematics could improve the odds. After years of research, he developed a "number-picking algorithm" based on a method he called "combinatorial condensation," according to The Hustle.

The strategy relied on a simple principle: identify lotteries where the jackpot exceeded the cost of buying every possible number combination. If enough tickets covering all combinations could be purchased, a profit could be guaranteed, the Independent reported.

Romanian-born mathematician Stefan Mandel. Photo courtesy of Stefan Mandel

In March 1965, Mandel persuaded a friend to buy lottery tickets with him and split any winnings 20-80 because he did not have enough money to fund the plan alone. Their first attempt was a success. The pair won the jackpot and several secondary prizes worth about $20,000. Mandel received roughly $4,000, equivalent to four years of income for an average Romanian family at the time.

"I’m a weekend mathematician, an accountant without too much education," he later told a Romanian magazine. "But mathematics properly applied can guarantee a fortune."

Mandel later emigrated to Australia, where he continued searching for lottery systems that fit his formula. He argued that "any high school math student could calculate the combinations." The challenge was not the mathematics but the logistics. Purchasing hundreds of thousands of tickets required both capital and an efficient system.

Over several years, he recruited hundreds of investors to form lottery syndicates and built an automated operation using computers and printers to generate massive numbers of tickets. The technology transformed the process. Instead of writing combinations by hand, Mandel could produce tickets automatically, dramatically reducing errors and increasing scale.

Throughout the 1980s, his syndicates targeted lotteries where jackpots exceeded the cost of purchasing every possible combination. The strategy helped them win 12 jackpots across Australia, along with roughly 400,000 smaller prizes, including a $1.1 million jackpot in 1986.

By 1989, opportunities in Australia had become increasingly limited, prompting Mandel to look elsewhere. His attention turned to Virginia, U.S., where he identified what he believed were favorable lottery rules. Players could buy unlimited tickets and print them at home. The game also used numbers from 1 to 44, creating about 7.1 million possible combinations, far fewer than many other U.S. lotteries.

Mandel calculated that the strategy would become profitable once the jackpot exceeded $25 million. His team spent about three months preparing for the operation. They printed all 7.1 million possible ticket combinations in Australia, shipped them to the U.S. and arranged bulk purchases through lottery retailers across Virginia, according to Business Insider.

By February 1992, Virginia's jackpot had risen above $27 million, triggering the plan. When the winning numbers were drawn, Mandel's syndicate secured the jackpot and more than $6 million in secondary prizes. Total winnings reached about $33 million, generating nearly $24 million in profit after ticket costs.

"I knew that I would win one first prize, six second prizes, 132 third prizes, and thousands of minor prizes," he told NPR's Planet Money producer Alex Goldmark in a podcast aired in 2016.

Mandel was investigated by the FBI, CIA, U.S. Secret Service and Interpol, but authorities found no evidence of wrongdoing. The Virginia Lottery subsequently paid out the jackpot. The case nevertheless prompted major changes to lottery regulations across the U.S. Authorities introduced limits on ticket purchases, required in-person sales and restricted large investment syndicates, effectively closing what became known as the "Mandel loophole."

A person holds a stack of lottery papers. Photo from Pexels

"It cannot be done anymore," NPR's Planet Money producer Alex Goldmark, who interviewed Mandel, told Business Insider. "The number of combinations have grown too much, you wouldn't be able to print the tickets, you wouldn't be able to buy them in time and you probably couldn't even do the math right to figure it out without making a mistake."

After paying investors and expenses, Mandel still retained a substantial fortune. He later attempted similar strategies in the U.K. and other countries but never matched his earlier success. "What we calculated to be the reality has changed," he wrote in a 1994 letter to investors. "It may not seem such a hot investment now."

He later disbanded his lottery syndicate and retired to a beach house in Vanuatu, a South Pacific island country known for its volcanoes and waterfalls, where he continues to live.

His former associate, Anithalee Alex, reflected on the story's extraordinary nature, saying: "You could not have written a script as good as this. This is one time real life was better than fiction."

Despite decades of speculation, Mandel has never disclosed the full details of his algorithm. As he told an enquiring Associated Press reporter in 1992, "That would be like Coca-Cola revealing their recipe."