IndexError: list index out of range

[bowlofred]

a_subj starts as a 1-element list. It gets t-1 extra elements as it goes through the for j in range(1, t) loop.

So if t is 3 or less, there will be 3 or less elements in a_subj. Then when you get to the print() statement, the request to print a_subj[3] will fail, since that index doesn't exist.

You are printing out the value of a_subj on line 21. What is the value?