811
811 is the United States telephone number to call before digging, so buried utilities can be marked.
- Odd
- Prime
Where 811 fits
Why 811 is special
One free call brings someone out to paint the ground where the gas, water and fibre run. It exists because striking an unmarked line is both common and occasionally fatal, and because before the single number there were dozens of regional ones nobody could be expected to know.
811 is part of
Factors & digit properties
- Divisors (2)
- 1, 811
- Prime factorisation
- 811
- Digit sum
- 10
- Digital root
- 1
Representations
- Decimal
- 811
- Scientific notation
- 8.110 × 10^2
Roman numerals
D C C C X I
Binary
1 1 0 0 1 0 1 0 1 1
1 × 512 + 1 × 256 + 0 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 1 × 8 + 0 × 4 + 1 × 2 + 1 × 1 = 811
Octal
1 4 5 3
1 × 512 + 4 × 64 + 5 × 8 + 3 × 1 = 811
Hexadecimal
3 2 b
3 × 256 + 2 × 16 + b × 1 = 811
Read as powers of two: 512 + 256 + 32 + 8 + 2 + 1 = 811.
In historical numeral systems
Egyptian
8 coils of rope, 1 hobble, 1 stroke
8 × 100 + 1 × 10 + 1 × 1 = 811. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 corner wedge + 3 vertical wedges (sixties place), 3 corner wedges + 1 vertical wedge (units place)
13 × 60 + 31 = 811. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
omega, then iota, then alpha, marked as a numeral
omega-iota-alpha + keraia
omega + iota + alpha written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
tav, then tav, then yod, then alef
tav-tav-yod-alef
tav (400) + tav (400) + yod (10) + alef (1) = 811, written in descending order.
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
- Twin prime
Related numbers & connections
811 appears in Numbers in law and public systems, the topic covering numbers that carry a documented law or public-systems fact.
Numbers Around Us
- appears inLaw and public systems
why?
Strength 0.50, confidence "high".
Law & regulation
The telephone number to call before digging is 811 (the United States). One call has every utility mark its buried lines on the ground, free, before excavation begins. It exists because the alternative — each digger contacting each utility — failed often enough to be a recurring cause of death.
DocumentedLaw & regulationGeography: the United States
Common questions
Is 811 a prime number?
Yes, 811 is prime — it has exactly two positive divisors: 1 and itself.
What are the factors of 811?
The factors of 811 are 1, 811.
What is 811 in Roman numerals?
811 in Roman numerals is DCCCXI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 1 reviewer-confirmed record, sourced and reviewed before publication.
Last reviewed: 15 July 2026