.
The recursive formula is (or can be taken in the form)
N(k) = 2*N(k-1) + 1, k = 2, 3, 4
for given values.
Please check it on your own that this formula really works.
When you complete checking and will prove for yourself that the formula works,
you may use it to move further and predict/calculate N(k) for k = 5, 6 and 7.
I leave this simple job for you.
You may report me about your progress.
Happy learning (!)
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Comment from student : i did get t7=1321 is that correct? thank you
My response : To answer your question, I prepared this Table below
T A B L E
k Given Calculated
numbers using the formula
------------------------------------
1 20 20
2 41 41
3 83 83
4 167 167
5 335
6 671
7 1343
First column is for index "k";
second column is the given numbers;
third column are the numbers calculated using the recursive formula.
From the Table, you see, that the formula correctly reproduces the given numbers.
Next, you see that the 7-th term is 1343, which does not coincide with your value.
So, your answer is INCORRECT.
Look for the error/errors in your computations.