Cui Shengjun has charted the past 100 lottery draws in China. Lines connecting all the numbers snake back and forth on a whiteboard on his wall.
"There definitely is a pattern. You just have to study it very carefully and I personally am something of an expert now," says the grey-haired manager of a Beijing convenience store.
Mr Cui's expertise apparently has its limits. He boasts of not having lost money, though concedes that he has also never won big.
Like millions of others across China, Mr Cui is hooked on the lottery. He plays instant games at video terminals, picks his daily "powerball" numbers and places weekly bets on football matches.
His story is little different from those of chronic gamblers the world over, apart from one major exception: gambling is illegal in China.
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Yet Mr Cui is no criminal: he plays the state-run lottery. In the late 1980s, looking to boost revenue, the government made an exception to a ban on all gambling that had been strictly enforced since Mao's day and created a lottery to support the development of a welfare system.
More than two decades on, this anomaly has grown into the biggest lottery boom the world has ever seen. Annual ticket sales are nearly 15,000-times higher than at their humble beginnings. China is on track to be the world's largest lottery market within this decade.
Ticket sales were up nearly 20 percent last year and the industry is worth $40 billion, ranking only behind the US, which pulls in more than $50 billion.
"As living conditions have improved, Chinese people have wanted to have more fun, to have a wider range of experiences. A stronger desire to gamble is part of that," says Cheng Haiping, a professor with the China lottery research center at Beijing Normal University.
Despite their traditional view of gambling as a social curse, China's Communist rulers now stand accused of doing too little to combat the ills that have come hand in hand with the runaway success of the lottery system.
We don't know where the money goes and we don't know how much goes to people playing the lottery.