Exponentiation confusion

[Adrian Klaver <adrian.klaver@xxxxxxxxxxx>]

In trying to answer an SO question I ran across this:

Postgres version 14.5

select 10^(-1 * 18);
 ?column?
----------
    1e-18

select 10^(-1 * 18::numeric);
      ?column?
--------------------
 0.0000000000000000


Same for power:

select power(10, -18);
 power
-------
 1e-18
(1 row)

select power(10, -18::numeric);
       power
--------------------
 0.0000000000000000


Why is the cast throwing off the result?

--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx