Sum of 2 Primes: 45 - (2 Digit Integer)?

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Discussion Overview

The discussion revolves around the problem of determining how many two-digit odd integers can be expressed as the sum of two prime numbers, and subsequently subtracting that count from 45. The focus includes mathematical reasoning and exploration of prime numbers.

Discussion Character

  • Mathematical reasoning, Exploratory, Debate/contested

Main Points Raised

  • Some participants propose that the solution involves counting two-digit odd numbers that can be expressed as the sum of two primes and then subtracting that count from 45.
  • One participant suggests that the answer is 24, claiming that about half of the odd two-digit numbers cannot be expressed as a sum of two primes, and that the sum must include the prime number 2 to yield an odd result.
  • Another participant questions the count of odd two-digit numbers where n-2 is prime, suggesting there are 21 such numbers.
  • There is a correction made by a participant regarding the count of odd two-digit numbers, indicating that they missed one in their previous assessment.

Areas of Agreement / Disagreement

Participants express differing views on the count of two-digit odd numbers that can be expressed as the sum of two primes, with no consensus reached on the exact number or the method of calculation.

Contextual Notes

Some assumptions about the definitions of prime numbers and the conditions for summation are not fully articulated, leading to potential ambiguity in the calculations presented.

Ilikebugs
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View attachment 6519 I think that we have to get all 2 digit odd numbers that can be expressed as the sum of 2 primes and subtract that from 45, so I think that the answer would be 45-(number of 2 digit integers n that are prime and have n-2 be prime as well)?
 

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Ilikebugs said:
I think that we have to get all 2 digit odd numbers that can be expressed as the sum of 2 primes and subtract that from 45, so I think that the answer would be 45-(number of 2 digit integers n that are prime and have n-2 be prime as well)?

$n$ doesn't have to be prime.
 
The question seems interesting. The answer is $24$. That is, about half of the odd 2-didit numbers cannot be expressed as a sum of two primes. The proof is simple. The sum if two primes must contain $2$, for otherwise the number cannot be odd. Thus, we have just check the primality of $n-2$ , where $n$ is any odd number.
 
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Arent there 21 odd 2 digit numbers where n-2 is prime, so its 24?
 
Ilikebugs said:
Arent there 21 odd 2 digit numbers where n-2 is prime, so its 24?

True, I missed one. Corrected though
 

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