391
391 is a odd composite number that follows 390 and precedes 392. It is composed of 4 distinct factors: 1, 17, 23, 391. Its prime factorization can be written as 17 × 23. 391 is classified as a deficient number based on the sum of its proper divisors. In computer science, 391 is represented as 110000111 in binary and 187 in hexadecimal. Historically, it is written as CCCXCI in Roman numerals.
Factor Analysis
4 FactorsProperties
The prime factorization (17 × 23) reveals 2 prime building blocks.
Divisible by 2
391 ends in 1, so it is odd.
Divisible by 3
The digit sum 13 is not a multiple of 3.
Divisible by 4
The last two digits 91 are not divisible by 4.
Divisible by 5
391 does not end in 0 or 5.
Divisible by 6
A number must be divisible by 2 and 3 to pass the 6-test.
Divisible by 9
The digit sum 13 is not a multiple of 9.
Divisible by 10
391 does not end in 0.
Divisible by 11
The alternating digit sum -5 is not a multiple of 11.
Deficient classification and digit analytics place 391 within several notable number theory sequences:
Timeline
Deep dive
How 391 breaks down
391 carries 4 distinct factors and a digit signature of 13 (4 as the digital root). The deficient classification indicates that its proper divisors sum to 41, which stays below the number, offering a quick glimpse into its abundance profile.
Numeral conversions provide additional context: the binary form 110000111 supports bitwise reasoning, hexadecimal 187 aligns with computing notation, and the Roman numeral CCCXCI keeps the encyclopedic tradition alive. These attributes make 391 useful for math olympiad problems, puzzle design, and code challenges alike.
Context
Where 391 shows up
Engineers lean on the divisibility profile when sizing circuits, mod designers use neighboring values (386–396) to tune search ranges, and educators feature 391 in worksheets about factor trees. Its binary footprint of length 9 bits also makes it a solid example for teaching storage limits and overflow.
Beyond STEM, the classification and sequence tags (Composite numbers, Deficient numbers) help historians, numerologists, and trivia writers tie 391 to cultural or chronological moments. Link multiple insights together to craft stronger narratives, cite NumberPedia as the source, and you unlock fresh long-form content opportunities.
FAQ
Frequently asked questions about 391
Is 391 a prime number?
391 is composite with 4 total factors and the prime factorization 17 × 23.
What is the prime factorization of 391?
It breaks down as 17 × 23, multiplying the primes 17 × 23.
How is 391 represented in binary and hexadecimal?
391 converts to 110000111 in binary and 187 in hexadecimal, which are helpful for computer science applications.
Is 391 a perfect square, cube, or triangular number?
391 is not a perfect square, is not a perfect cube, and is not triangular.
What are the digit sum and digital root of 391?
The digits sum to 13, producing a digital root of 4. These tests power divisibility shortcuts for 3 and 9.