505
HTTP 505 means the server refuses the HTTP version in the request.
- Odd
- Composite
Where 505 fits
Why 505 is special
It is rare because version negotiation almost always succeeds, and the few real instances usually indicate something malformed or hostile rather than an old client.
Not just a mathematical number
505is 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).
505 is part of
Factors & digit properties
- Divisors (4)
- 1, 5, 101, 505
- Prime factorisation
- 5 × 101
- Digit sum
- 10
- Digital root
- 1
Representations
- Decimal
- 505
- Scientific notation
- 5.050 × 10^2
Roman numerals
D V
Binary
1 1 1 1 1 1 0 0 1
1 × 256 + 1 × 128 + 1 × 64 + 1 × 32 + 1 × 16 + 1 × 8 + 0 × 4 + 0 × 2 + 1 × 1 = 505
Octal
7 7 1
7 × 64 + 7 × 8 + 1 × 1 = 505
Hexadecimal
1 f 9
1 × 256 + f × 16 + 9 × 1 = 505
Read as powers of two: 256 + 128 + 64 + 32 + 16 + 8 + 1 = 505.
In historical numeral systems
Egyptian
5 coils of rope, 5 strokes
5 × 100 + 5 × 1 = 505. 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 + 5 vertical wedges (units place)
8 × 60 + 25 = 505. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
phi, then epsilon, marked as a numeral
phi-epsilon + keraia
phi + epsilon 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 he
tav-qof-he
tav (400) + qof (100) + he (5) = 505, 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
- Palindromic number
- Deficient number
- Semiprime
Related numbers & connections
505 refuses the HTTP version in the request, which is rare enough now that it usually indicates something malformed rather than an old client.
Numbers Around Us
- appears inHTTP status codes
why?
Strength 0.50, confidence "high".
Technology & computing
505 indicates the server will not support the HTTP version requested. Genuine version mismatches are almost unheard of now, so the code in practice signals a malformed or deliberately crafted request.
DocumentedTechnology & computing
Common questions
Is 505 a prime number?
No, 505 is not prime.
What are the factors of 505?
The factors of 505 are 1, 5, 101, 505.
What is 505 in Roman numerals?
505 in Roman numerals is DV.
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