If you look closely at your Out[8] you will see that the lower case i you refer to is different than the usual lower case i. It is Mathematicas output for I. (When the code is pasted in here as a code block, it comes through as I.)
IN with no space between I and N is a symbol. With a space in between, it is I multiplied by N. With 3I or 3N, Mathematica understands it as multiplication, since symbol names cannot begin with a number.
The multiplication example you give can be expanded if you want to see the multiplication carried out. But note that lower case i is not the imaginary unit.
Also note that * is not needed to express multiplication. It is also best to begin all symbol names with lower case, since Mathematica uses upper case for reserved words. For example, N is a built in function for evaluating an argument to a numerical value
.
In[1]:= (1 + I) (1 - 3 I)
Out[1]= 4 - 2 I
In[2]:= IN
Out[2]= IN
In[3]:= I N
Out[3]= I N
In[4]:= (1 + i) (1 - 3 i)
Out[4]= (1 - 3 i) (1 + i)
In[5]:= Expand[(1 + i) (1 - 3 i)]
Out[5]= 1 - 2 i - 3 i^2
