Table.concat

table.concat (table [, sep [, i [, j]]])

Given an array where all elements are strings or numbers, returns table[i]..sep..table[i+1] ··· sep..table[j]. The default value for sep is the empty string, the default for i is 1, and the default for j is the length of the table. If i is greater than j, returns the empty string.

Select

Unpack

Lua Manual - Concatenation Operator (..)

Lua Manual - The length operator #

Lua Manual - Variadic Expressions (...)