= Marin Mersenne
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<Marin Mersenne> was a <mathematician> and scientific correspondent whose network helped <Pierre de Fermat>, <René Descartes> and other researchers exchange questions and results. He studied <number theory> and the <acoustics> of vibrations of <mechanical strings>.https://mathshistory.st-andrews.ac.uk/Biographies/Mersenne/[Biography, correspondence network and laws of vibrating strings]{ref} A <Mersenne number> has the form $2^p-1$; for it to be a <Mersenne prime>, $p$ must be a <prime number>, although that condition is not sufficient: $2^{11}-1=23\cdot89$. For an ideal stretched <mechanical string>, the fundamental <frequency> is $f=(2L)^{-1}\sqrt{T/\mu}$, relating the audible pitch to the length $L$, <tension> $T$ and mass per unit length $\mu$.
\Image[https://upload.wikimedia.org/wikipedia/commons/c/cd/Marin_Mersenne_by_Balthasar_Moncornet.jpg]
{title=Portrait of <Marin Mersenne>}
{description=Engraving dated 1654 on https://commons.wikimedia.org/wiki/File:Marin_Mersenne_by_Balthasar_Moncornet.jpg[Wikimedia Commons], which identifies the artwork as public domain.}
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