Number of ways of expressing n as positive integers

In summary, the conversation discusses the concept of expressing a positive integer as a sum of positive integers, represented by the notation S_n. It is mentioned that S_n is equal to the sum of S_{n-1} and S_{n-2} with the additional constraint of S_1+1. The conversation also includes a request for clarification and a hint on how to approach the proof of this equation.
  • #1
dr hannibal
10
0
sorry for the many threads

Let S_n denote the number of ways of expressing n as positive integrs..
S_1=1 , s_2=2, s_3=4 ..

Prove that
[tex]S_n=S_{n-1}+S_{n-2} ---S_1+1 [/tex]

no idea to prove that :
 
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  • #2
Sorry, but to me it's not clear what your question means. What does it mean to express a positive integer as positive integers? I can only think of one way to express 3 as a positive integer, namely by 3. Can you show how S_3 = 4?

Your notation in the equation is also confusing. What is the meaning of three consecutive minus signs?
 
  • #3
I assume that you mean [itex]S_n[/itex] is the number of ways to express [itex]n[/itex] as a sum of positive integers, where orders matters.

Consider the different cases for the last integer in the sum, all of which are disjoint, since order matters. There are [itex]n[/itex] different cases.

Explicitly: if the last integer is 1, then the rest of the integers sum to [itex]n-1[/itex]...
 
  • #4
nicksauce said:
Sorry, but to me it's not clear what your question means. What does it mean to express a positive integer as positive integers? I can only think of one way to express 3 as a positive integer, namely by 3. Can you show how S_3 = 4?

Your notation in the equation is also confusing. What is the meaning of three consecutive minus signs?

it means 3 can be written as 1+1+1 , 2+1, 1+2, 3 so 4 different ways..
 
  • #5
tmccullough said:
I assume that you mean [itex]S_n[/itex] is the number of ways to express [itex]n[/itex] as a sum of positive integers, where orders matters.

Consider the different cases for the last integer in the sum, all of which are disjoint, since order matters. There are [itex]n[/itex] different cases.

Explicitly: if the last integer is 1, then the rest of the integers sum to [itex]n-1[/itex]...
Yup that's what I meant
for your hint how would I use notation to represent it ..just one line would be enough

c, its just I have been grappling with this question for far too long and have not made any headway..

Thanks
 

Related to Number of ways of expressing n as positive integers

1. What is the concept of expressing a number as a sum of positive integers?

The concept of expressing a number as a sum of positive integers is known as "partitioning". It involves breaking down a given number into smaller positive integers that add up to the original number.

2. How many ways can a number be expressed as a sum of positive integers?

The number of ways a number can be expressed as a sum of positive integers is known as its "partition function". The exact number of ways varies for each number and can be calculated using mathematical formulas or by using computer algorithms.

3. Are there any patterns or rules for partitioning a number into positive integers?

Yes, there are certain patterns and rules that can be observed when partitioning a number into positive integers. For example, a number can only be partitioned into as many positive integers as its value. Also, the order of the integers in the partition does not matter.

4. Is there any significance to the number of ways a number can be partitioned into positive integers?

Yes, the number of ways a number can be partitioned into positive integers can have significant applications in various fields such as number theory, combinatorics, and computer science. It can also be used to solve various mathematical problems and puzzles.

5. Can all numbers be partitioned into positive integers?

Yes, all positive integers can be partitioned into positive integers, including 1 which can only be partitioned as 1 itself. However, negative numbers and fractions cannot be partitioned into positive integers.

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