Prime number
A prime number is a number with a certain universally recognizable characteristic.

When captured by unknown aliens in 2366, Captain Jean-Luc Picard signaled the first six prime numbers by pushing the same button in sequence, hoping to prove to his captors that he was intelligent. ()

Astronomers on Kelemane's planet also signaled prime numbers to the "Sky Ship" in an effort to communicate. Their attempts were successful. ()

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de: Primzahl
Mathematics