How do you express the sequence below as a recursively defined function 4, 11, 25, 53, 109,...?

sdentatoiz

sdentatoiz

Answered question

2022-09-08

How do you express the sequence below as a recursively defined function 4, 11, 25, 53, 109,...?

Answer & Explanation

Everett Mclaughlin

Everett Mclaughlin

Beginner2022-09-09Added 16 answers

Generally the functions are defined explicitly by a formula in terms of the variable, say x.
We can also define functions recursively: in terms of the same function of a smaller variable building on itself and in the case of sequences, this is generally the number of the term.
For example here, first term is a 1 = 4 .
Observe that second term a 2 = 11 is obtained by adding 7 to first term
and third term a 3 = 25 obtained by adding 14 to second term.
Hence we can say a 1 = 4
a 2 = 4 + 7 ( 2 - 1 ) = 11
and a 3 = a 2 + 7 ( 3 - 1 ) = 11 + 7 × 2 = 21
Hence we can say a n = a n - 1 + 7 ( n - 1 ) , where a 1 = 4

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