Which Prime Numbers Make $2p^3 + 4p^2 - 3p + 12$ a Fifth Power?

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In summary, prime numbers are positive integers that have exactly two positive divisors and are only divisible by 1 and themselves. Fifth powers are numbers that have been raised to the fifth power, meaning they have been multiplied by themselves five times. The relationship between prime numbers and fifth powers is that there are infinitely many prime numbers that can be expressed as the sum of two fifth powers, also known as the "Prime Power Conjecture." POTW #462 is focusing on these two concepts as a challenging and interesting mathematical problem. Some real-life applications of prime numbers and fifth powers include cryptography, computer security, generating random numbers, and their role in number theory and mathematics.
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anemone
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Here is this week's POTW:

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Find all prime numbers $p$ such that $2p^3+4p^2-3p+12$ is the fifth power of an integer.

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  • #2
No one answered last two week's POTW. (Sadface) However, you can find the suggested solution as follows:
Denote $f(n)=2n^3+4n^2-3n+12$. The following table shows the remainders of $n^2,\,n^3,\,n^5$ and $f(n)$ upon division by 11:
\begin{equation*}
\begin{array}{c|c|c|c|c}
n & 0 & 1 & 2 &3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 \\
\hline
n^2 & 0 & 1 & 4 & 9 & 9 & 3 & 3 & 5 & 9 & 1 & 1 \\
n^3 & 0 & 1 & 8 & 5 & 9 & 4 & 7 & 2 & 6 & 3 & 10 \\
n^5 & 0 & 1 & 10 & 1 & 1 & 1 & 10 & 10 & 10 & 1 & 10 \\
f(n) & 1 & 4 & 5 & 5 & 5 & 6 & 9 & 4 & 3 & 7 & 6 \\
\end{array}
\end{equation*}

As one can see from the table, the only remainders upon division by 11 that the fifth power of an arbitrary integer $n$ can give are 0, 1, and 10. On the other hand, integers of the form $f(n)$ give only remainders 1, 3, 4, 5, 6, 7, and 9 upon division by 11, whereby the remainder is 1 only if $n$ is divisible by 11. Consequently, $f(p)$ can be the fifth power of an integer only if $p$ is divisible by 11. As $p$ is prime, the only possibility is $p=11$. And indeed, $f(11)=2\cdot 11^3+4\cdot 11^2-3\cdot 11+12=3125=5^5$.
 

Related to Which Prime Numbers Make $2p^3 + 4p^2 - 3p + 12$ a Fifth Power?

1. What are prime numbers?

Prime numbers are positive integers that have exactly two factors, 1 and the number itself. In other words, they can only be divided by 1 and itself without leaving a remainder.

2. How do you determine if a number is a prime number?

One way to determine if a number is prime is to check if it is divisible by any number other than 1 and itself. Another method is to use the Sieve of Eratosthenes, which involves creating a list of numbers and eliminating all multiples of the numbers until only prime numbers remain.

3. What is the significance of fifth powers in mathematics?

Fifth powers, or numbers raised to the fifth power, are important in mathematics because they often appear in equations and formulas, particularly in algebra and geometry. They are also used in number theory, cryptography, and other areas of mathematics.

4. What is the connection between prime numbers and fifth powers in POTW #462?

In POTW #462, the challenge is to find all prime numbers that can be expressed as the sum of two fifth powers. This connection between prime numbers and fifth powers is known as the Hardy-Littlewood conjecture, which states that every integer can be expressed as the sum of at most five fifth powers.

5. Why is the study of prime numbers and fifth powers important?

The study of prime numbers and fifth powers is important in mathematics because it helps us understand the fundamental properties of numbers and their relationships. It also has practical applications in fields such as cryptography, where prime numbers are used to create secure codes and algorithms.

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