9,000 was referenced to an episode of Dragon Ball Z in which Vegeta and Nappa are very suprised at Goku's suprise boost of attack power, creating one of the most well-known internet memes "It's over 9,000!!!"[1]

For this reason, 9,000 was used as the first entry in the xkcd forum thread "My number is bigger!".

It is also the number of possible four-digit postal codes which don't start with the digit 0.

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