Number dictionary · Exact arithmetic
421: factors and number facts
four hundred twenty-one is an odd number and is prime. Its 2 positive divisors form 1 factor pair.
Number JD Editorial Team · Updated 2026-10-08
- In words
- four hundred twenty-one
- Roman numeral
- CDXXI
- Prime factorization
- 421
- Digital root
- 7
All factors of 421
A positive factor divides 421 with no remainder. In ascending order, the complete list is:
1, 421
Factor pairs
- 1 × 421 = 421
Each pair describes an arrangement of 421 items into equal rows. The pairs have different row and column counts; 421 cannot make a square array of whole items.
Divisor totals
- Positive divisors
- 2
- Sum of all divisors
- 422
- Sum excluding 421
- 1
- Classification
- deficient
421 is deficient because its proper divisors add to 1, which is less than 421.
Prime factorization of 421
421 = 421
Repeated division, step by step
- 421 ÷ 421 = 1
Multiply the prime divisors in these steps to reconstruct 421. Each prime in this factorization occurs once. The divisor-count calculation is (1 + 1) = 2.
The preceding prime is 419. The next larger prime is 431. To check 421 for primality, it is sufficient to test possible divisors from 2 through 20.
Learn the factorization method421 in words, Roman numerals and other bases
| Representation | Value |
|---|---|
| English (US style) | four hundred twenty-one |
| Roman numeral | CDXXI |
| Binary (base 2) | 110100101 |
| Octal (base 8) | 645 |
| Decimal (base 10) | 421 |
| Hexadecimal (base 16) | 1A5 |
Check the binary conversion
Read 110100101 from right to left using place values 1, 2, 4, 8 and successive powers of two. Keep the values whose bit is 1:
256 + 128 + 32 + 4 + 1 = 421
Check the hexadecimal conversion
1 × 16^2 + 10 × 16^1 + 5 × 16^0 = 421
Hexadecimal uses A through F for digit values 10 through 15. These notations represent the same quantity; changing the base does not change the integer.
Square, cube and square root of 421
- 421 squared
- 421 × 421 = 177,241
- 421 cubed
- 421 × 421 × 421 = 74,618,461
- Square root
- ≈ 20.518285
- Simplified radical
- √421
421 lies between 400 (20²) and 441 (21²), so it is not a perfect square. It is not a perfect cube.
421 is not triangular: no positive whole-number k satisfies k(k + 1) / 2 = 421.
Distinguish a square from a square rootMultiplication table for 421
These are the first twelve positive multiples. Unlike the finite factor list, the sequence of multiples continues without an upper limit.
Divisibility checks
| Divide by | Whole quotient | Remainder | Divides exactly? |
|---|---|---|---|
| 2 | 210 | 1 | No |
| 3 | 140 | 1 | No |
| 4 | 105 | 1 | No |
| 5 | 84 | 1 | No |
| 6 | 70 | 1 | No |
| 7 | 60 | 1 | No |
| 8 | 52 | 5 | No |
| 9 | 46 | 7 | No |
| 10 | 42 | 1 | No |
| 11 | 38 | 3 | No |
| 12 | 35 | 1 | No |
For example, 421 = 7 × 60 + 1. A remainder of zero is what makes a divisor a factor.
Digit sum and digital root of 421
421 contains 3 decimal digits. Its digit sum is 4 + 2 + 1 = 7.
- 421: 4 + 2 + 1 = 7
The digital root is 7. Reversing its digits gives 124; it is not a decimal palindrome. Digit patterns depend on the notation being used.
Digital-root arithmetic always finishes at a single digit for a positive integer. Some numerology methods stop at 11, 22 or 33 instead; that is a separate interpretive convention.
Fractions and a worked comparison
As a fraction of 100, 421/100 simplifies to 421/100 by dividing both terms by their greatest common divisor, 1. Its decimal value is 4.21. Because the numerator exceeds the denominator, this value is greater than one.
The greatest common divisor of 421 and 12 is 1. Their least common multiple is 5052. The identity GCD × LCM = 421 × 12 = 5052 checks both results.
Work through GCF and LCMQuestions about 421
What are the factors of 421?
The positive factors are 1, 421. There are 2 factors, including 1 and 421.
Is 421 a prime number?
Yes. The only positive divisors of 421 are 1 and 421.
How do you write 421 in Roman numerals?
421 is CDXXI in standard subtractive Roman numeral notation.
What is the binary representation of 421?
421 in decimal is 110100101 in base 2. Adding its active place values gives 256 + 128 + 32 + 4 + 1 = 421.
Methods and reference definitions
Number JD calculates each result from the integer on this page. Positive factors are enumerated in pairs; repeated division gives the prime factorization; place values verify base conversions. Decimal square roots are rounded to six places when irrational.
NUMBER JOURNAL / JD
A reflective note on 421
Meaning varies by tradition and personal experience. One sighting is not evidence of what will happen next.
The digits of 421 add to 7. That arithmetic result is separate from the cultural symbolism of the pattern. If this number matters to you, write down what you noticed and choose one grounded action rather than treating the sighting as a prediction.