1991
1991 is the year the Soviet Union dissolved and the World Wide Web opened to the public.
- Odd
- Composite
Where 1991 fits
Why 1991 is special
1991 ended one order and quietly began another. The USSR was formally dissolved in December after a failed August coup. In August the same year, Tim Berners-Lee posted the World Wide Web project publicly for the first time — the moment the web stopped being a CERN tool and became something anyone could join.
Same number, different meanings
How 1991 is understood across different contexts — never implying one meaning because of another.
- Mathematics
1991 ended one order and quietly began another. The USSR was formally dissolved in December after a failed August coup. In August the same year, Tim Berners-Lee posted the World Wide Web project publicly for the first time — the moment the web stopped being a CERN tool and became something anyone could join.
- History
In 1991, the Soviet Union dissolved, and the World Wide Web became publicly available.
- Technology & computing
On 6 August 1991 Tim Berners-Lee posted a summary of the World Wide Web project to a public newsgroup, with instructions for obtaining the software. That posting, rather than the 1989 proposal, is the point at which anyone outside CERN could join — four months before the Soviet Union was dissolved.
1991 is part of
Factors & digit properties
- Divisors (4)
- 1, 11, 181, 1991
- Prime factorisation
- 11 × 181
- Digit sum
- 20
- Digital root
- 2
Representations
- Decimal
- 1991
- Scientific notation
- 1.991 × 10^3
Roman numerals
M C M X C I
MCMXCI uses the subtractive pair XC: ten before a hundred — a hundred minus ten.
Binary
1 1 1 1 1 0 0 0 1 1 1
1 × 1,024 + 1 × 512 + 1 × 256 + 1 × 128 + 1 × 64 + 0 × 32 + 0 × 16 + 0 × 8 + 1 × 4 + 1 × 2 + 1 × 1 = 1,991
Octal
3 7 0 7
3 × 512 + 7 × 64 + 0 × 8 + 7 × 1 = 1,991
Hexadecimal
7 c 7
7 × 256 + c × 16 + 7 × 1 = 1,991
Read as powers of two: 1,024 + 512 + 256 + 128 + 64 + 4 + 2 + 1 = 1,991.
In historical numeral systems
Egyptian
1 lotus, 9 coils of rope, 9 hobbles, 1 stroke
1 × 1,000 + 9 × 100 + 9 × 10 + 1 × 1 = 1,991. 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), 1 corner wedge + 1 vertical wedge (units place)
33 × 60 + 11 = 1991. 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
- Palindromic number
- Deficient number
- Semiprime
Related numbers & connections
1991 is a year in the 20th century, in the 1990s.
The web was published in 1991 and became usable by the public in 1993, when CERN placed it in the public domain and Mosaic displayed images alongside text.
View 1993 →Numbers Around Us
- appears inHistorical years
why?
Strength 0.50, confidence "high".
- appears alongside1969
why?
Strength 0.50, confidence "high".
History
In 1991, the Soviet Union dissolved, and the World Wide Web became publicly available.
DocumentedHistoryGeography: globalPeriod: 1991
Technology & computing
On 6 August 1991 Tim Berners-Lee posted a summary of the World Wide Web project to a public newsgroup, with instructions for obtaining the software. That posting, rather than the 1989 proposal, is the point at which anyone outside CERN could join — four months before the Soviet Union was dissolved.
DocumentedTechnology & computingPeriod: 6 August 1991
Common questions
Is 1991 a prime number?
No, 1991 is not prime.
What are the factors of 1991?
The factors of 1991 are 1, 11, 181, 1991.
What is 1991 in Roman numerals?
1991 in Roman numerals is MCMXCI. XC is subtractive: ten before a hundred — a hundred minus ten. Written additively it would be MDCCCCLXXXXI, which Roman inscriptions used freely — the strict subtractive form is a later convention.
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