SHANGHAI (Reuters) - Is it a coincidence that China’s most-watched stock index fell 64.89 points on the anniversary of the June 4, 1989, crackdown on student-led democracy protests centered on Beijing’s Tiananmen Square?

Most likely, say the experts.

Trying to work the Shanghai Composite Index .SSEC to hit a specific number would take Herculean muscle and precision, requiring a trader, or traders, to buy and sell huge quantities of blue-chip stocks with an improbable degree of exactness.

On Monday, it would have been exceedingly difficult, said a seasoned Chinese stock analyst who declined to be identified. The market tanked 2.7 percent in reaction to weak U.S. jobs data and economic instability in Europe, producing 87 billion yuan ($13.66 billion) worth of turnover in more than 90,000 transactions over the course of the day.

“In theory it’s possible, though difficult, to manipulate the index through large cap stocks,” said the stocks analyst.

The Shanghai stock market fell a bizarre 64.89 points on Monday, the anniversary of the bloody crackdown on protesters in Tiananmen Square on June 4, 1989, or 6-4-89.

In another twist, the Shanghai Composite Index .SSEC opened at 2346.98 points on the 23rd anniversary of the killings. The numbers 46.98 could be read as June 4, 1989, backwards.

If getting the index to settle on those figures through trades can be ruled out, could the trading system itself have been hacked?

Computerized trading platforms for the NASDAQ exchange were repeatedly hacked in 2011, for example. However, the hackers were targeting sensitive company information, not seeking to manipulate an index to express a subtle political protest.

It is difficult to estimate how vulnerable the Shanghai exchange system is to hacking, said Gregory So, head of sales for northeast Asia for SunGard, a financial systems software provider.

“We really don’t know what kind of system they use in China and how tight it is. I think for the Shanghai Stock Exchange, it’s a proprietary system they developed for themselves.”

SENSITIVE TO NUMBERS

Bai Shuo, chief technology officer of the Exchange, told Reuters there was “no problem” with trading systems on Monday but said the exchange was looking into the matter.

It may seem unlikely that anyone would try to commemorate the June 4th anniversary in such an unconventional way, but numbers are watched closely in China, where numerological superstition is wide and deep, reaching into everything from the selection of phone numbers to the scheduling of major events to expressions of dissent.

Thus authorities aren’t taking chances: China’s censors blocked access to the term “Shanghai stock market” and to the index numbers themselves on microblogs on Monday, as they maintained tight control over the internet to suppress mention of the Tiananmen events.

Censors even prevented users from changing their photos to prevent the upload of photos related to Tiananmen.

Numbers have been used to worry the government before. A Chinese numerologist suggested in an online blog post that a series of disasters preceding the Beijing Olympics indicated that the games - scheduled to open on August 8, 2008 - were doomed to disaster.

For example, he said the May 12, 2008, earthquake that rocked China’s Sichuan province, killing nearly 80,000 people, was an expression of numerological dissatisfaction by the heavens.

Five, for May, plus one plus two equals eight, he said, adding that the quake happened 88 days before the start of the Beijing Olympics, which started on August 8 at 8:08 pm.

Earlier that year, a blizzard hit on January 25 - a month-day combination that also adds up to eight - leaving millions of households without power, heating or water for days and stranding millions of migrant workers hoping to head home for a holiday.