## Can someone help me figure out a recursive formula for this?

Sequences, counting (including probability), logic and truth tables, algorithms, number theory, set theory, etc.
noobzilla
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### Can someone help me figure out a recursive formula for this?

I GIVE UP, seriouosly i've tried so many ways to figure this out but i just can't seem to see the pattern

Find the next two numbers in each sequence.

A) -1, 1 , 3 , 7 , 15 , ______ , _______

B) 3, 1, 2 , -1 , 3 , -4 , ______, _______

C) 16, 24, 36 , 54 , 81, ______, ______

just to show you I'm really trying hard, the next two terms for the second sequences are as follows (according to my calculations of course):

3, 1, 2 , -1 , 3 , -4 , 7, -11, 18

stapel_eliz
Posts: 1628
Joined: Mon Dec 08, 2008 4:22 pm
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For some general techniques, try here.
Find the next two numbers in each sequence.

A) -1, 1 , 3 , 7 , 15 , ______ , _______
What are the differences between the terms? What is 2*2? What is 2*4?
B) 3, 1, 2 , -1 , 3 , -4 , ______, _______
What are the differences? What is the sum of |-2| and |1|? What is the sum of |1| and |-3|? (I get the same next terms as you do, by the way.)
C) 16, 24, 36 , 54 , 81, ______, ______
What are the differences? What is the value of 2*22? What is the value of 3*22? What is the value of 2*32? What is the value of 3*32?

noobzilla
Posts: 15
Joined: Wed Oct 07, 2009 4:24 pm
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### Re: Can someone help me figure out a recursive formula for this?

THANK YOU SO MUCHH!!

I get it all now, thnx a lot, for the last two i was able to find formulas that work, just like the one you hinted me to see, it works both ways, but i'll use yours cause it's simpler, and the first one, GOD I swear I couldn't see the pattern in it

But Thanks Again, I'm very grateful for your help!