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I don't know about Japanese, but in Chinese, all the numbers have words that can be said extremely quickly - si, qi, etc. Because our working memory is implemented as a 2 second loop of audio, this allows Chinese people to have a working memory that's closer to 10 items instead of the famous 'seven plus or minus two' that English speakers have. In 'Outliers' Malcolm Gladwell posits this as part of the reason why asians often seem to be better at math.