User blog:! cook the lettuce/Extend This Notation!

Welcome to my second competition! Instead of creating a number, this time around you will be extending a function.

Here are, again, the rules: With all that in mind: I will start.
 * 1) Work with all of the rules of the previous entries.
 * 2) You can't suddenly change the notation from what it starts as.
 * 3) always corresponds to the end of the array.
 * 4) All rules from my number competition apply.

[] = [0] = 1

[a] = 15^n

[#, a, b] = [#, [a, [a...[a]...]]] with b nestings

[#, 1] = [#]

[#, +, a] = [#, (+^1), a] = [#, a, a...a, a] with a repetitions

[#, (+^a), b] = [#, (+^a-1), (+^a-1)...(+^a-1), (+^a-1), a]