Answer:
a(4) = 21
Explanation:
Given the recursion relation a(1) = 1, a(n) = a(n-1)² -4, you want the value of a(4).
Recursion
The quickest way to find the first few terms of a recursively-defined sequence is to evaluate the recursion relation.
The attached calculator display shows the first 4 terms of the sequence.
a(4) = 21
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Additional comment
Here's an example of evaluating the given relation using a(3) = 5:
a(4) = (a(3))² -4 = 5² -4 = 25 -4 = 21
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