> > That said, I don’t know how to pronounce “3e5”

> "Three to the exponent of five." Or "Three Exponent Five." Or "Three Exp Five."

Somehow, you need to distinguish between 3^5 (=243), 3 x e^5 (=~445.24), and 3 x 10^5 (=300,000).

I'd pronounce "3e5" and "three times ten to the 5" in most cases.

> 3^5 (=243)

Three to the power of five.

> 3 x e^5

Three times the fifth power of e. Or Three times e's fifth power.

> 3 x 10^5 (=300,000).

Three to the exponent of five.

A calculator user once suggested "decapower." I think exponent and "EXP" are comfortable and easy to say and are ingrained to most old school calculator users. Which is also why I think "e's fifth power" can be a more natural sequence.