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 July 11th, 2011, 01:57 PM #1 Member   Joined: May 2011 Posts: 38 Thanks: 0 recursive definitions construct a recursive definition for each: a) the sequence 2, 10, 50, 250... b) the number of ways a sequence of 1's and 2's will sum to n. For example, x3 = 3 since 2+1, 1+1+1, and 1+2 all sum to 3. Notice that 1+2 is not the same as 2+1, since the first and second elements of each sum are different c) the number of ways to stank n red, white, green, and blue poker chips so that there are no two consecutive blue poker chips.
 July 11th, 2011, 02:08 PM #2 Senior Member   Joined: Jan 2011 Posts: 106 Thanks: 0 Re: recursive definitions So what have you come up with so far, and where exactly you seem to be stuck in?
 July 11th, 2011, 02:37 PM #3 Senior Member   Joined: Jul 2011 Posts: 227 Thanks: 0 Re: recursive definitions For example exercice a): Important here is to examine if these sequence is arithmetic or geometric, if you know that you'Il be able to construct a recursive formula.
 July 12th, 2011, 08:39 AM #4 Global Moderator     Joined: Nov 2006 From: UTC -5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms Re: recursive definitions I'm partial to a(n) = a(n-4) for #1, but I suspect that the desired answer is more like a(n) = k * a(n-1). What value of k can you choose to make this true? (This is related to Hooman's hint.)
 July 13th, 2011, 03:02 PM #5 Member   Joined: May 2011 Posts: 38 Thanks: 0 Re: recursive definitions for a) I got f(0) = 2 f(n+1) = f(n) x 5 could that work?
 July 13th, 2011, 04:00 PM #6 Member   Joined: May 2011 Posts: 38 Thanks: 0 Re: recursive definitions i can't seem to find the sequence for the last one: the number of ways to stack n red, white, green and blue poker chips so that there are no two consecutive blue poker chips
July 14th, 2011, 08:32 AM   #7
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Re: recursive definitions

Quote:
 Originally Posted by lamhmh for a) I got f(0) = 2 f(n+1) = f(n) x 5 could that work?
Correct!

July 14th, 2011, 08:46 AM   #8
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Re: recursive definitions

Quote:
 Originally Posted by lamhmh the number of ways to stack n red, white, green and blue poker chips so that there are no two consecutive blue poker chips
Step 1: stack the red, white, and green chips.
Step 2: decide where to insert the blue chips. If there are n-b chips already stacked, there are n-b+1 places to choose from.

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