What operation is denoted by this subscript notation?

Question

What operation is denoted here?

$$11_3$$

I believe the answer to this is 4.

Answer 1

Base, or radix.

$11_3$ is the number $4$ written in base $3$: $$ 11_3 = 1\cdot 3^1+1\cdot 3^0 = 3+1=4 $$ A small nitpick: it is not technically an operation, but a notation.

Answer 2

It's not an operation - it's a sign for what base the number is expressed in.

$11_3=4_{10}$.