A lottery in the Philippines, in which 433 people won the jackpot, surprised the citizens, but also prompted the authorities to start an investigation into the case, reports BBC.

This is the largest number of people who have ever won the main prize of the "Grand Lotto", local media reports.

The winning combination for last weekend's 236 million peso ($4 million) jackpot was a series of numbers that were divisible by nine.

Philippines Senate Minority Leader Coco Pimentel called for an investigation into the "suspicious" results.

One expert stated that 10 million bets were placed on the assumption, and he estimated the probability of there being that many winners to be "1 in 1 followed by 1.224 zeroes".

"I don't know a name for this number because it's so big." The number of molecules in the known universe has 80 zeros," said Guido David, professor of mathematics at the University of the Philippines.

Lottery participants select six numbers from 1 to 55. To win the jackpot, a player must match all six numbers drawn by the lottery operator.

“These games are authorized by the Republic of the Philippines. Therefore, we need to maintain and protect the integrity of these games of chance,” Pimentel said.

On Sunday, Melquiades Robles, director general of the Philippine Charity Sweepstakes Office (PSCO), said there was no wrongdoing and noted that people in the Philippines tend to bet on a sequence of numbers.

"Many stick to their number." It's not only good to be loyal to your wives and husbands, but it's also good to be loyal to your numbers," Robles said at a press conference.

The PCSO also shared photos and videos of people collecting their prize money in Mandaluyong City, close to the capital Manila.

"I've been betting on numbers 6,7,8 and 9 for many years and I'm grateful to finally win," said one winner.

Terence Tao, a mathematics professor at the University of California, Los Angeles, told the BBC that a pattern like this being a winning series of numbers is rare "for any lottery".

"But there are hundreds of lotteries every day around the world, and statistically it wouldn't be surprising that every few decades, one of these lotteries would show an unusual pattern," he said.

"It's similar to how in any given hand of poker it's unlikely to get a straight flush, but if you look at hundreds of thousands of hands at once, then it actually becomes quite likely to get a flush," he added.