$$ The notation (1,2,3) is a permutation function f with the property f(1) = 2, f(2) = 3, f(3) = 1.

$$ And the notation (1,2) is a permutation function g with the property g(1) = 2, g(2) = 1, g(3) = 3. (Whenever an integer is omitted, that means the function fixes that integer, lke 3 in the previous example)

$$ So (1,2,3)(1,2) is a notation f*g (composition of f and g). Can you calculate (1,2,3)(1,2) now?