exponentiation
/ĕk″spə-nĕn″shē-ā′shən/
noun
- (mathematics, arithmetic, uncountable) The process of calculating a power by multiplying together a number of equal factors, where the exponent specifies the number of factors to multiply.
- (mathematics, arithmetic, countable) A mathematical problem involving exponentiation.
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I think "e to the x" or "the exponential of x" are both fine. I might even use "e of x."
When I read it out loud, I prefer saying e to the $\rm x$ because it is a quick phrase and means the same as e raised to the $x$th power. Albeit, it still differs from person-to-person.
The references say "two to the sixteenth power" or "two to the power of sixteen" but that is only done in very formal speech. Ironically, in actual mathematical usage, the formal pronunciation is not that common.
The more common way to say it (in math class or in a mathematical presentation) is a ellipsis of the first:
two to the sixteenth
or just as commonly
two to the sixteen
depending on how rapid speech you are using.
Of course there are some special cases: x2 is "x squared", x3 is "x cubed". x1 or x0 are mathematically jarring if written alone (they are often, when mathematically allowed, written just "x" and "one"), but if forced would be "x to the one" and "x to the zero", never as an ordinal (it is a solecism to say "x to the first" and way too informal to say .
For example, a polynomial x109 + 9x5 − 2x2 is most likely pronounced:
x to the hundred and nine plus nine x to the fifth minus two x squared.
(or "hundred and ninth"; both are equally possible here). If it were x101 — see discussion here —, you just don't say "one hundred first".)
If variables are involved, the ordinal is not used. xy is
x to the y
(that is, not appending the ordinal suffix '-th').
I would use two raised to the sixteenth power which is the full version. Although when people are saying a big numeral expression they skip it to two to the sixteenth.