Nth term of sequence 1, 3, 15, 61, 213

Question

Nth term of sequence 1, 3, 15, 61, 213 and also 6th term ...thx

Answer 1

Hi Era,

 

This is a messy sequence question. I really just tested different options and came up with this:

a_n = 3ⁿ - n² - n 

As you see it is a geometric sequence. 

So, the 6th terms is

a₆ = 3⁶ - 6² - 6 

= 729 - 36 - 6

= 687