A “strange and unusual” lottery draw in the Philippines that led to 433 people winning with a combination of numbers that were all multiples of nine has prompted suspicion and calls for an investigation. A prize of 236m pesos (£3.55m) will be split between the winners, with each receiving about 545,000 pesos, subject to taxes, for picking the numbers 09, 45, 36, 27, 18 and 54 during the Philippine Charity Sweepstakes Office (PCSO) grand lotto draw on Saturday. It is the highest number of people to have won the government-sponsored Grand Lotto’s jackpot, according to media reports. Dr Guido David, professor of mathematics at the University of the Philippines, said in a Twitter post that the probability of having 433 winners was “1 out of 1 followed by 1,224 zeros”. The result has prompted speculation on social media that the draw was rigged, as well as calls from politicians for an inquiry. The senate minority leader, Aquilino “Koko” Pimentel III, described the result as “strange and unusual” and said in a statement that he would call for an audit of the PCSO’s gaming activities to ensure their integrity and protect the public. “Many were really puzzled and surprised because statistically speaking, this is a very rare event,” Pimentel said. “I will file a resolution, because this is my concern, these lotto games are authorised by the Republic of the Philippines. Therefore, we need to maintain and protect the integrity of these gambling games that we have authorised,” he added. Marcelino Libanan, the house minority floor leader representative, also called for an inquiry. The PCSO has shared pictures on social media of people queueing to collect their prizes, holding their winning tickets. Officials from the office rejected allegations of irregularities, saying that observers were present to monitor pre-draw procedures. Machines were inspected, they said, as were the weighing and loading of balls. “We would like to assure the public that the PCSO is honest about its responsibility and mandate to conduct games that are trustworthy, have integrity, utmost sincerity and transparency,” said Melquiades Robles, the PCSO general manager, in comments reported by the Rappler news website. In a statement on Facebook, Robles added: “Lottery is a game of chance, nothing is definite and it is uncontrollable. To the 433 new jackpot winners, it pays to be loyal.”