00000000000000000021e800c1e8df51b22c1588e5a624bea17e9faa34b2dc4a, or simply 21e800, is the hash of Bitcoin block #528249 that was mined on June 19th, 2018 at 12:32:27 UTC.

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After a tweet by Mark Wilcox with the hashtag #00000000000000000021e800c1e8df51b22c1588e5a624bea17e9faa34b2dc4a, a discussion arose on Twitter about the meaning of the block.

^{[4] [12]} The discourse centers around the first 24 numbers of the hash.

The sequence 21e800 appears after the first 18 0s in the hash.

21e8 signifies An Exceptionally Simple Theory of Everything, which is also known as E8 theory.

E8 theory is a physics preprint proposing a basis for a unified field theory, which attempts to describe all known fundamental interactions in physics and to stand as a possible theory of everything.

^[13] Some speculate that whoever mined the hash is a time traveling quantum computer, possibly Satoshi himself, and have made memes to express their conclusions.

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Others view the hash as merely a coincidence.

^[14] Assistant Professor of Electrical and Computer Engineering at the University of Illinois, Urbana-Champaign Andrew Miller says the hash is nothing special and said "There’s nothing to say about this really, it’s just a joke...

There are 16 possibilities for each of the first 4 (nonzero) digits.

The probability that a given block begins with the particular string 21e8 is 1/(161616*16), which is about one in one-hundred thousand.

The bitcoin blockchain has over 500,000 blocks.”

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