2001
2001 is the year of the September 11 attacks, and the year Wikipedia launched.
- Odd
- Composite
Where 2001 fits
Why 2001 is special
2001 is remembered almost entirely for one September morning, and the security, legal and foreign-policy consequences that followed for decades. It is also the year Wikipedia began in January — an unrelated event that turned out to reshape how a generation looks things up.
Same number, different meanings
How 2001 is understood across different contexts — never implying one meaning because of another.
- Mathematics
2001 is remembered almost entirely for one September morning, and the security, legal and foreign-policy consequences that followed for decades. It is also the year Wikipedia began in January — an unrelated event that turned out to reshape how a generation looks things up.
- History
In 2001, the September 11 attacks killed nearly three thousand people and reshaped global security policy.
- Technology & computing
Wikipedia launched on 15 January 2001, initially as a side project to feed a peer-reviewed encyclopedia that never took off. Within a year the side project had far outgrown the parent. Its founding predates the September attacks that define the year in most other respects by eight months.
2001 is part of
Factors & digit properties
- Divisors (8)
- 1, 3, 23, 29, 69, 87, 667, 2001
- Prime factorisation
- 3 × 23 × 29
- Digit sum
- 3
- Digital root
- 3
Representations
- Decimal
- 2001
- Scientific notation
- 2.001 × 10^3
Roman numerals
M M I
Binary
1 1 1 1 1 0 1 0 0 0 1
1 × 1,024 + 1 × 512 + 1 × 256 + 1 × 128 + 1 × 64 + 0 × 32 + 1 × 16 + 0 × 8 + 0 × 4 + 0 × 2 + 1 × 1 = 2,001
Octal
3 7 2 1
3 × 512 + 7 × 64 + 2 × 8 + 1 × 1 = 2,001
Hexadecimal
7 d 1
7 × 256 + d × 16 + 1 × 1 = 2,001
Read as powers of two: 1,024 + 512 + 256 + 128 + 64 + 16 + 1 = 2,001.
In historical numeral systems
Egyptian
2 lotuses, 1 stroke
2 × 1,000 + 1 × 1 = 2,001. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
3 corner wedges + 3 vertical wedges (sixties place), 2 corner wedges + 1 vertical wedge (units place)
33 × 60 + 21 = 2001. Places are separated by a space on the tablet, with the higher place written first.
Systems that simply cannot reach this value are left out. Where a script needs a font most readers do not have, the reading is given instead of the glyphs — see number systems for each system in full.
Other mathematical patterns
- Deficient number
- Harshad (Niven) number
- Lucky number (mathematical sieve)
Related numbers & connections
2001 is a year in the 21st century, in the 2000s.
The American emergency number and the date of the 2001 attacks are written with the same three digits, distinguished in print only by punctuation.
View 911 →History
In 2001, the September 11 attacks killed nearly three thousand people and reshaped global security policy.
DocumentedHistoryGeography: globalPeriod: 2001
Technology & computing
Wikipedia launched on 15 January 2001, initially as a side project to feed a peer-reviewed encyclopedia that never took off. Within a year the side project had far outgrown the parent. Its founding predates the September attacks that define the year in most other respects by eight months.
DocumentedTechnology & computingPeriod: 15 January 2001
Common questions
Is 2001 a prime number?
No, 2001 is not prime.
What are the factors of 2001?
The factors of 2001 are 1, 3, 23, 29, 69, 87, 667, 2001.
What is 2001 in Roman numerals?
2001 in Roman numerals is MMI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026