[MO] Example using operation between + and *

[Gottfried]

<Not directly connected with tetration but with fractional-indexed binary operations...>

In the math-overflow I came across that nice question, which connects the "half-indexed" operation "between add and multiply" with Sophie-Germain-primes.

http://mathoverflow.net/questions/48638/...ain-primes

A tiny, but nice and surprising piece...

Gottfried