“Irregular transaction, please try again later,” the app says. Chen notes, another permutation involving the date and the year—1989—won’t work either.

In fact, blocking “64” is a common tactic, even if it means the hyper-paranoid Chinese authorities end up casting their net a little wide. Tweets with the numeral are being deleted on Sina Weibo, China’s Twitter-like social media platform, at the moment, according to FreeWeibo.com (along with the Chinese words for Oriental Star and shipwreck). The politically delicate tweets that the censors have recently deleted include one reporting July Brent crude futures falling to $64.88 a barrel and another about a 64-year-old American woman returning lost money that she found on the street.

This kind of censorship overreach isn’t limited to the anniversary of Tiananmen. Google’s blog flagged two examples in 2012. The first saw the censors block the character  (jiang, which is a common surname and also means “river”)—probably due to gossip surrounding the former president Jiang Zemin. It caused error messages for the zillion places and names that feature that character, including a leading hotel chain, a popular tourist town, the mobile phone carrier for an entire province, and the Yangtze River, to name a few.

Something similar happened with searches involving 周 (zhou, a common surname and that of now-disgraced former leader Zhou Yongkang, though it otherwise means week). Searches for pop star Jay Chou and comedian Stephen Chow, and even the words for “weekend” and days of the week fritzed.

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