\myheading{Semiprime numbers}

Semiprime is a product of two prime numbers.

An interesting property of semiprime:

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In 1974 the Arecibo message was sent with a radio signal aimed at a star cluster. It consisted of 1679 binary digits intended to be interpreted as a 23×73 bitmap image. The number 1679 = 23×73 was chosen because it is a semiprime and therefore can only be broken down into 23 rows and 73 columns, or 73 rows and 23 columns.
\end{lstlisting}

( \url{https://en.wikipedia.org/wiki/Semiprime} )