Number dictionary · Exact arithmetic
721: factors and number facts
seven hundred twenty-one is an odd number and is composite. Its 4 positive divisors form 2 factor pairs.
Number JD Editorial Team · Updated 2026-10-08
- In words
- seven hundred twenty-one
- Roman numeral
- DCCXXI
- Prime factorization
- 7 × 103
- Digital root
- 1
All factors of 721
A positive factor divides 721 with no remainder. In ascending order, the complete list is:
1, 7, 103, 721
Factor pairs
- 1 × 721 = 721
- 7 × 103 = 721
Each pair describes an arrangement of 721 items into equal rows. The pairs have different row and column counts; 721 cannot make a square array of whole items.
Divisor totals
- Positive divisors
- 4
- Sum of all divisors
- 832
- Sum excluding 721
- 111
- Classification
- deficient
721 is deficient because its proper divisors add to 111, which is less than 721.
Prime factorization of 721
721 = 7 × 103
Repeated division, step by step
- 721 ÷ 7 = 103
- 103 ÷ 103 = 1
Multiply the prime divisors in these steps to reconstruct 721. Each prime in this factorization occurs once. The divisor-count calculation is (1 + 1) × (1 + 1) = 4.
The preceding prime is 719. The next larger prime is 727. The factor list above explains why 721 is composite.
Learn the factorization method721 in words, Roman numerals and other bases
| Representation | Value |
|---|---|
| English (US style) | seven hundred twenty-one |
| Roman numeral | DCCXXI |
| Binary (base 2) | 1011010001 |
| Octal (base 8) | 1321 |
| Decimal (base 10) | 721 |
| Hexadecimal (base 16) | 2D1 |
Check the binary conversion
Read 1011010001 from right to left using place values 1, 2, 4, 8 and successive powers of two. Keep the values whose bit is 1:
512 + 128 + 64 + 16 + 1 = 721
Check the hexadecimal conversion
2 × 16^2 + 13 × 16^1 + 1 × 16^0 = 721
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 721
- 721 squared
- 721 × 721 = 519,841
- 721 cubed
- 721 × 721 × 721 = 374,805,361
- Square root
- ≈ 26.851443
- Simplified radical
- √721
721 lies between 676 (26²) and 729 (27²), so it is not a perfect square. It is not a perfect cube.
721 is not triangular: no positive whole-number k satisfies k(k + 1) / 2 = 721.
Distinguish a square from a square rootMultiplication table for 721
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 | 360 | 1 | No |
| 3 | 240 | 1 | No |
| 4 | 180 | 1 | No |
| 5 | 144 | 1 | No |
| 6 | 120 | 1 | No |
| 7 | 103 | 0 | Yes |
| 8 | 90 | 1 | No |
| 9 | 80 | 1 | No |
| 10 | 72 | 1 | No |
| 11 | 65 | 6 | No |
| 12 | 60 | 1 | No |
For example, 721 = 7 × 103 + 0. A remainder of zero is what makes a divisor a factor.
Digit sum and digital root of 721
721 contains 3 decimal digits. Its digit sum is 7 + 2 + 1 = 10.
- 721: 7 + 2 + 1 = 10
- 10: 1 + 0 = 1
The digital root is 1. Reversing its digits gives 127; 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, 721/100 simplifies to 721/100 by dividing both terms by their greatest common divisor, 1. Its decimal value is 7.21. Because the numerator exceeds the denominator, this value is greater than one.
The greatest common divisor of 721 and 12 is 1. Their least common multiple is 8652. The identity GCD × LCM = 721 × 12 = 8652 checks both results.
Work through GCF and LCMQuestions about 721
What are the factors of 721?
The positive factors are 1, 7, 103, 721. There are 4 factors, including 1 and 721.
Is 721 a prime number?
No. 721 is composite: 7 × 103 = 721.
How do you write 721 in Roman numerals?
721 is DCCXXI in standard subtractive Roman numeral notation.
What is the binary representation of 721?
721 in decimal is 1011010001 in base 2. Adding its active place values gives 512 + 128 + 64 + 16 + 1 = 721.
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 721
Meaning varies by tradition and personal experience. One sighting is not evidence of what will happen next.
The digits of 721 add to 10. 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.