# Math Help - little help for a little person

1. ## little help for a little person

5,100,20,400, _ _ _ _ what numbers follow ,what is the rule,also what type of number sequence is it,many thanks elliott age 9.

2. Originally Posted by finfish
what type of number sequence ,5,100,20,400 many thanks
well, it's not arithmetic since there is no common difference
it's not geometric since there is no common ratio
chances are it's a recursive sequence.

here is what it is:

the sequence is defined recursively as follows:

a_1 = 5, a_2 = 100, a_n = a_(n - 2) * 4 for n >or=3

many thanks but i have worked it out , 5x4=20 100x4=400

4. Originally Posted by finfish
many thanks but i have worked it out , 5x4=20 100x4=400
that does not define a sequence

5. Originally Posted by finfish
5,100,20,400, _ _ _ _ what numbers follow ,what is the rule,also what type of number sequence is it,many thanks elliott age 9.
5,100,20,400,80,1600 ------
the sequense is like this because 5*4=20,100*4=400,then 20*4=80and400*4=1600.and so on