## Primal scream

2^{43112609}-1 is the world’s largest known prime number. Written down in full it’s 12,978,189 digits long. That would take a long time to read out, let alone scream. It would be much simpler to type it out. Maybe.

Reproduced in real life this number would stretch for up to 32km. Depending on the typeface. Different fonts apparently produce markedly different results.

Prime numbers are also, apparently, useful for things other than cryptography.

In case you’re wondering, prime numbers aren’t just the stuff of academic longhairs: like typefaces, they have interesting properties that make them strangely useful. The classical example comes from mechanical engineering, where two meshed gears will wear most evenly if each has a coprime number of teeth, since this evenly distributes the possible ways in which they interact (thereby minimizing the effects of any irregularities.) Some have suggested that 13- and 17-year cicadas each follow prime numbered life cycles in order to ensure that their populations compete as little as possible, coexisting only once every 221 years.