Prime numbers vs consecutive natural numbers.

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Discussion Overview

The discussion revolves around the properties of prime numbers in relation to their representation as sums of consecutive natural numbers. Participants explore whether prime numbers, excluding the number 2, can be expressed solely as the sum of two consecutive natural numbers, and the implications of this on the understanding of odd primes.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant claims that all odd numbers can be expressed as a sum of consecutive natural numbers, providing examples to illustrate this.
  • Another participant argues that the sum of $k$ consecutive natural numbers is either $0 \pmod{k}$ or $0 \pmod{k/2}$, suggesting that the only plausible candidates for sums involving odd primes are $k = 1$ and $k = 2$.
  • A different participant reiterates that the sum of $k$ consecutive natural numbers is $0 \pmod{k}$, indicating that $k = 1$ is the only plausible candidate and provides an example with the prime number 7.
  • One participant prompts a reconsideration of the previous claims, indicating potential oversight in the discussion.
  • A later post suggests that the question should be reframed to demonstrate that only prime numbers (except for 2) can be expressed as the sum of two consecutive natural numbers.

Areas of Agreement / Disagreement

Participants express differing views on the representation of prime numbers as sums of consecutive natural numbers, with no consensus reached on the validity of the claims made. The discussion remains unresolved regarding the conditions under which prime numbers can be expressed in this manner.

Contextual Notes

Participants have not fully explored the implications of their assumptions regarding the sums of consecutive natural numbers and their modular properties. There are also unresolved mathematical steps in the reasoning presented.

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An easy question.

All "odd" number can be expressed as a sum of consecutive natural numbers.

Example:

35=17+18

35=5+6+7+8+9

35=2+3+4+5+6+7+8Question:

Demonstrate that prime numbers (except for the "2"), can only be expressed as the sum of two consecutive natural numbers.
 
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Re: prime numbers vs consecutive natural numbers.

Elementary. Sum of $k$ consecutive natural numbers is either $0 \pmod{k}$ or $0 \pmod{k/2}$ so the only plausible candidates are $k = 1$ and $k = 2$ which is easy to verify for odd primes.
 
Last edited:
Re: prime numbers vs consecutive natural numbers.

mathbalarka said:
Sum of $k$ consecutive natural numbers is $0 \pmod{k}$ so the only plausible candidate is $k = 1$ which is easy to verify for odd primes.

7=3+4 \rightarrow{} k=2
 
Re: prime numbers vs consecutive natural numbers.

Look at it again.
 
the question should be
Demonstrate that only prime numbers (except for the "2"), can be expressed as the sum of two consecutive natural numbers only.
let the number of numbers be n and 1st number a+1

then sum of numbers= an + n(n+1)/2

it is integer
if n is odd (n+1)/2 is integer so it is divsible by n

if n is even an and n(n+1)/2 is divisible by n/2

so if n > 2 and odd it is not prime as divsible by n

if n > 2 and even it is divisible by n/2(which is >= 2) so not prime
 
Last edited:

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