501
501 is the starting score in a standard game of darts, counted down to exactly zero.
- Odd
- Composite
Where 501 fits
Why 501 is special
501 is chosen to be awkward. Players count down from it and must finish on a double, so the odd starting total means the last dart cannot simply halve a round number — it forces a checkout to be planned several throws ahead. The highest possible finish is 170: treble 20, treble 20, bullseye.
501 connects to:
- 180 — appears alongside
- http status codes — appears in
- darts maximum score — is associated with
Same number, different meanings
How 501 is understood across different contexts — never implying one meaning because of another.
- Mathematics
501 is chosen to be awkward. Players count down from it and must finish on a double, so the odd starting total means the last dart cannot simply halve a round number — it forces a checkout to be planned several throws ahead. The highest possible finish is 170: treble 20, treble 20, bullseye.
- Technology & computing
501 is the HTTP status code for a request method the server does not support at all — distinct from 405, which means the method is understood but not allowed for that resource, and from 500, which means the server tried and failed. It is a 5xx code, so it reports a server-side limitation rather than a client mistake. In practice it is rare, because most servers implement the whole standard method set.
- Law & regulation
Section 501(c) of the United States Internal Revenue Code lists organisations exempt from federal income tax, and its third subsection — 501(c)(3) — covers charitable, religious, educational and scientific bodies. It is cited constantly because it is the paragraph that both grants the exemption and makes donations tax-deductible, and because it carries the restriction on political campaigning that periodically puts American charities in the news. The designation is a US federal tax status and has no equivalent force elsewhere.
- Media & popular culture
Levi Strauss & Co. assigned the lot number 501 to its copper-riveted waist overalls around 1890, when the company began numbering its products, and the garment has carried it ever since. The number identifies a stock line rather than describing anything — there is no design meaning in the digits — which is precisely what makes it unusual: an internal warehouse code that became one of the most recognisable product names in the world.
- Sport
A game of darts must finish on a double, so the closing throw is constrained rather than free. Starting from 501 rather than 500 means the total is odd, so a player cannot simply halve their way down and must plan a checkout several darts ahead — the arithmetic is part of the skill. The highest possible finish is 170.
Not just a mathematical number
501is also used in ways where ordinary arithmetic doesn't apply — each listed below with what genuinely does and doesn't follow from it.
- Mathematical number
A genuine quantity — its mathematical properties (prime, square, factors, and so on) are real facts about it.
A genuine quantity that ordinary arithmetic applies to — it can be prime, even, a perfect square, added to another number meaningfully, and so on.
- Code
Also used as a code — HTTP status codes.
An assigned identifier from a fixed registry or standard — its digits don't represent an amount, and arithmetic on it is meaningless (HTTP status 404 + 1 is not a 'better' status; it's a different, unrelated code).
501 is part of
Factors & digit properties
- Divisors (4)
- 1, 3, 167, 501
- Prime factorisation
- 3 × 167
- Digit sum
- 6
- Digital root
- 6
Representations
- Decimal
- 501
- Scientific notation
- 5.010 × 10^2
Roman numerals
D I
Binary
1 1 1 1 1 0 1 0 1
1 × 256 + 1 × 128 + 1 × 64 + 1 × 32 + 1 × 16 + 0 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 501
Octal
7 6 5
7 × 64 + 6 × 8 + 5 × 1 = 501
Hexadecimal
1 f 5
1 × 256 + f × 16 + 5 × 1 = 501
Read as powers of two: 256 + 128 + 64 + 32 + 16 + 4 + 1 = 501.
In historical numeral systems
Egyptian
5 coils of rope, 1 stroke
5 × 100 + 1 × 1 = 501. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
8 vertical wedges (sixties place), 2 corner wedges + 1 vertical wedge (units place)
8 × 60 + 21 = 501. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
phi, then alpha, marked as a numeral
phi-alpha + keraia
phi + 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 qof, then alef
tav-qof-alef
tav (400) + qof (100) + alef (1) = 501, 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
- Semiprime
Related numbers & connections
The two numbers a darts commentator says most. 501 is where every leg starts and 180 is the maximum a single visit can score, so the game is largely the arithmetic of getting from one to the other and still finishing on a double.
View 180 →501 is the score every darts leg starts from, and the reason the maximum three-dart visit of 180 matters as much as it does.
Numbers Around Us
- appears alongside180
why?
Strength 0.50, confidence "high".
- appears inHTTP status codes
why?
Strength 0.50, confidence "high".
Other connections
- is associated withMaximum three-dart score
why?
Strength 0.50, confidence "high".
Technology & computing
501 is the HTTP status code for a request method the server does not support at all — distinct from 405, which means the method is understood but not allowed for that resource, and from 500, which means the server tried and failed. It is a 5xx code, so it reports a server-side limitation rather than a client mistake. In practice it is rare, because most servers implement the whole standard method set.
DocumentedTechnology & computing
Law & regulation
Section 501(c) of the United States Internal Revenue Code lists organisations exempt from federal income tax, and its third subsection — 501(c)(3) — covers charitable, religious, educational and scientific bodies. It is cited constantly because it is the paragraph that both grants the exemption and makes donations tax-deductible, and because it carries the restriction on political campaigning that periodically puts American charities in the news. The designation is a US federal tax status and has no equivalent force elsewhere.
DocumentedLaw & regulationGeography: United States
Media & popular culture
Levi Strauss & Co. assigned the lot number 501 to its copper-riveted waist overalls around 1890, when the company began numbering its products, and the garment has carried it ever since. The number identifies a stock line rather than describing anything — there is no design meaning in the digits — which is precisely what makes it unusual: an internal warehouse code that became one of the most recognisable product names in the world.
DocumentedMedia & popular culturePeriod: c. 1890 onwards
Mathematics
501 = 3 × 167, and the odd total is the entire point of the darts convention. Because a leg must close on a double, the final score must be even; starting from an odd number forces at least one odd score along the way, so a player cannot descend by halving and must arrive at a checkout deliberately. Shorter formats use 301 and 701 for the same reason, and all three are one more than a round number.
DocumentedMathematics
Sport
A game of darts must finish on a double, so the closing throw is constrained rather than free. Starting from 501 rather than 500 means the total is odd, so a player cannot simply halve their way down and must plan a checkout several darts ahead — the arithmetic is part of the skill. The highest possible finish is 170.
DocumentedSport
Common questions
Why does darts start at 501?
Because the odd number is what makes the finish difficult. A leg must close on a double, so the last score has to be even; starting from an odd total means a player cannot simply halve their way down and must plan a checkout several darts ahead. The highest possible finish is 170 — treble 20, treble 20, bullseye. Shorter formats use 301 and 701 for the same reason.
What does 501(c)(3) mean?
It is the paragraph of the United States Internal Revenue Code that exempts charitable, religious, educational and scientific organisations from federal income tax and makes donations to them tax-deductible. It also carries the restriction on political campaigning that periodically puts American charities in the news. It is a US federal tax status with no equivalent force elsewhere.
Is 501 a prime number?
No, 501 is not prime.
What are the factors of 501?
The factors of 501 are 1, 3, 167, 501.
What is 501 in Roman numerals?
501 in Roman numerals is DI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 5 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026