520
520 is a non-standard status code used by Cloudflare for an unexplained origin server failure.
- Even
- Composite
Where 520 fits
Why 520 is special
520 is not in any RFC. Cloudflare invented the 52x range to describe failures between its edge and a customer's origin server, and 520 is the catch-all: the origin returned something empty, unexpected or malformed. Seeing one means the problem is behind the proxy, not at it.
Not just a mathematical number
520is 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).
Factors & digit properties
- Divisors (16)
- 1, 2, 4, 5, 8, 10, 13, 20, 26, 40, 52, 65, 104, 130, 260, 520
- Prime factorisation
- 2^3 × 5 × 13
- Digit sum
- 7
- Digital root
- 7
Representations
- Decimal
- 520
- Binary
- 1000001000
- Octal
- 1010
- Hexadecimal
- 208
- Roman numeral
- DXX
- Scientific notation
- 5.200 × 10^2
Other mathematical patterns
- Abundant number
Related numbers & connections
530 accompanies a second, more specific error and is Cloudflare's least self-explanatory code — it always requires reading the paired one.
View 530 →Technology & computing
The 52x range is Cloudflare's own invention and appears in no RFC or IANA registry. That matters when reading them: a 520 says something went wrong between Cloudflare's edge and the origin server, information a standard 502 does not carry — but only if you are behind Cloudflare in the first place.
DocumentedTechnology & computing
Common questions
Is 520 a prime number?
No, 520 is not prime.
What are the factors of 520?
The factors of 520 are 1, 2, 4, 5, 8, 10, 13, 20, 26, 40, 52, 65, 104, 130, 260, 520.
What is 520 in Roman numerals?
520 in Roman numerals is DXX.
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: 3 August 2026