Converting to Factorial Notation

Oct 13, 2025 by pinkandtrash.com 68 views

Introduction

In the realm of number theory, the study of prime numbers and their properties has led to numerous breakthroughs and discoveries. However, the study of products of numbers, particularly those with a large number of factors, has also yielded interesting results. In this article, we will delve into the problem of finding the number of zeroes at the end of a product, specifically the product of numbers from 5 to 30 raised to the power of their respective values plus one.

The Product Notation

The given product notation is:

β=∏_{n=5}^{30} n^{n+1}

This notation represents the product of numbers from 5 to 30, where each number is raised to the power of its value plus one. For example, the first term in the product is $5^6$ , which means 5 raised to the power of 6.

Converting to Factorial Notation

The first thought when encountering this product notation is to convert it into the factorial notation, which is a more familiar and manageable form. The factorial notation is defined as:

n! = n × (n-1) × (n-2) × ... × 2 × 1

Using this notation, we can rewrite the product as:

β=5^6⋅6^7⋅7^8... 30^{31}=5^6⋅6^... 29^{30}⋅30^{31}

This form is more recognizable and can be used to apply the Legendre formula, which provides a way to calculate the number of trailing zeroes in a factorial.

The Legendre Formula

The Legendre formula states that the number of trailing zeroes in a factorial is given by:

v_p(n!) = \sum_{k=1}^{\infty} \left\lfloor \frac{n}{p^k} \right\rfloor

where $v_p(n!)$ is the number of trailing zeroes in $n!$ , $p$ is a prime number, and $k$ is a positive integer.

Applying the Legendre Formula

To apply the Legendre formula to our product, we need to calculate the number of trailing zeroes in each term. Since the product is a product of numbers from 5 to 30, we will focus on the prime factors of these numbers.

The prime factors of the numbers from 5 to 30 are:

5: 5
6: 2, 3
7: 7
8: 2, 2
9: 3, 3
10: 2, 5
11: 11
12: 2, 2, 3
13: 13
14: 2, 7
15: 3, 5
16: 2, 2, 2, 2
17: 17
18: 2, 3, 3
19: 19
20: 2, 2, 5
21: 3, 7
22: 2, 11
23: 23
24: 2, 2, 2, 3
25: 5, 5
26: 2, 13
27: 3, 3, 3
28: 2, 2, 7
29: 29
30: 2, 3, 5

Calculating the Number of Trailing Zeroes

Using the Legendre formula, we can calculate the number of trailing zeroes in each term. We will focus on the prime factors of the numbers from 5 to 30.

For the prime factor 5, we have:

v_5(5^6) = \left\lfloor \frac{5}{5} \right\rfloor + \left\lfloor \frac{5}{5^2} \right\rfloor + \left\lfloor \frac{5}{5^3} \right\rfloor + \left\lfloor \frac{5}{5^4} \right\rfloor + \left\lfloor \frac{5}{5^5} \right\rfloor + \left\lfloor \frac{5}{5^6} \right\rfloor = 1 + 0 + 0 + 0 + 0 + 0 = 1

Similarly, for the prime factor 2, we have:

v_2(6^7) = \left\lfloor \frac{6}{2} \right\rfloor + \left\lfloor \frac{6}{2^2} \right\rfloor + \left\lfloor \frac{6}{2^3} \right\rfloor + \left\lfloor \frac{6}{2^4} \right\rfloor + \left\lfloor \frac{6}{2^5} \right\rfloor + \left\lfloor \frac{6}{2^6} \right\rfloor + \left\lfloor \frac{6}{2^7} \right\rfloor = 3 + 1 + 0 + 0 + 0 + 0 + 0 = 4

We can continue this process for all the prime factors of the numbers from 5 to 30.

The Final Result

After calculating the number of trailing zeroes in each term, we can add up the results to get the total number of trailing zeroes in the product.

The final result is:

v_5(5^6) + v_2(6^7) + v_7(7^8) + ... + v_{30}(30^{31}) = 1 + 4 + 1 + ... + 0 = 10

Therefore, the number of zeroes at the end of the product is 10.

Conclusion

In this article, we have explored the problem of finding the number of zeroes at the end of a product, specifically the product of numbers from 5 to 30 raised to the power of their respective values plus one. We have used the Legendre formula to calculate the number of trailing zeroes in each term and added up the results to get the total number of trailing zeroes in the product. The final result is 10.

References

Legendre, A. (1808). Essai sur la théorie des nombres. Paris: Firmin-Didot.
Hardy, G. H., & Wright, E. M. (1979). An introduction to the theory of numbers. Oxford University Press.

Appendix

The following is a list of the prime factors of the numbers from 5 to 30:

5: 5
6: 2, 3
7: 7
8: 2, 2
9: 3, 3
10: 2, 5
11: 11
12: 2, 2, 3
13: 13
14: 2, 7
15: 3, 5
16: 2, 2, 2, 2
17: 17
18: 2, 3, 3
19: 19
20: 2, 2, 5
21: 3, 7
22: 2, 11
23: 23
24: 2, 2, 2, 3
25: 5, 5
26: 2, 13
27: 3, 3, 3
28: 2, 2, 7
29: 29
30: 2, 3, 5
Q&A: Number of Zeroes at the End of a Product =============================================

Q: What is the product notation used in this article?

A: The product notation used in this article is:

β=∏_{n=5}^{30} n^{n+1}

This notation represents the product of numbers from 5 to 30, where each number is raised to the power of its value plus one.

Q: How is the product notation converted to factorial notation?

A: The product notation is converted to factorial notation by rewriting each term as a factorial. For example, the first term $5^6$ is rewritten as $5! \cdot 6! \cdot 7! \cdot ... \cdot 30!$ .

Q: What is the Legendre formula used for?

A: The Legendre formula is used to calculate the number of trailing zeroes in a factorial. It is given by:

v_p(n!) = \sum_{k=1}^{\infty} \left\lfloor \frac{n}{p^k} \right\rfloor

where $v_p(n!)$ is the number of trailing zeroes in $n!$ , $p$ is a prime number, and $k$ is a positive integer.

Q: How is the Legendre formula applied to the product notation?

A: The Legendre formula is applied to each term in the product notation by calculating the number of trailing zeroes in each term. This is done by finding the prime factors of each term and using the Legendre formula to calculate the number of trailing zeroes.

Q: What is the final result of the calculation?

A: The final result of the calculation is 10, which is the number of zeroes at the end of the product.

Q: What are the prime factors of the numbers from 5 to 30?

A: The prime factors of the numbers from 5 to 30 are:

5: 5
6: 2, 3
7: 7
8: 2, 2
9: 3, 3
10: 2, 5
11: 11
12: 2, 2, 3
13: 13
14: 2, 7
15: 3, 5
16: 2, 2, 2, 2
17: 17
18: 2, 3, 3
19: 19
20: 2, 2, 5
21: 3, 7
22: 2, 11
23: 23
24: 2, 2, 2, 3
25: 5, 5
26: 2, 13
27: 3, 3, 3
28: 2, 2, 7
29: 29
30: 2, 3, 5

Q: What is the significance of the Legendre formula in this article?

A: The Legendre formula is significant in this article because it provides a way to calculate the number of trailing zeroes in a factorial. This is useful in calculating the number of zeroes at the end of a product, such as the product notation used in this article.

Q: What are some potential applications of the Legendre formula?

A: The Legendre formula has potential applications in various fields, such as:

Number theory: The Legendre formula can be used to calculate the number of trailing zeroes in a factorial, which is useful in number theory.
Combinatorics: The Legendre formula can be used to calculate the number of trailing zeroes in a product, which is useful in combinatorics.
Computer science: The Legendre formula can be used to calculate the number of trailing zeroes in a product, which is useful in computer science.

Q: What are some potential limitations of the Legendre formula?

A: The Legendre formula has potential limitations, such as:

Complexity: The Legendre formula can be complex to apply, especially for large numbers.
Accuracy: The Legendre formula may not be accurate for large numbers, especially if the number of trailing zeroes is large.

Q: What are some potential future directions for research on the Legendre formula?

A: Some potential future directions for research on the Legendre formula include:

Developing more efficient algorithms for applying the Legendre formula.
Investigating the accuracy of the Legendre formula for large numbers.
Exploring potential applications of the Legendre formula in other fields.