25,519
25,519 names Curve25519, the elliptic curve whose arithmetic is done modulo 2²⁵⁵ − 19.
- Odd
- Composite
Why 25,519 is special
The name is the exponent and the subtrahend run together. The curve was designed so that every possible input is a valid key and no parameter is unexplained — a response to earlier standard curves whose constants nobody could account for. It is now the default for SSH keys and for Signal's key exchange.
Factors & digit properties
- Divisors (6)
- 1, 13, 151, 169, 1963, 25519
- Prime factorisation
- 13^2 × 151
- Digit sum
- 22
- Digital root
- 4
Representations
- Decimal
- 25519
- Scientific notation
- 2.552 × 10^4
Roman numerals
Roman numerals as modelled here goes up to 3,999.
Binary
1 1 0 0 0 1 1 1 0 1 0 1 1 1 1
1 × 16,384 + 1 × 8,192 + 0 × 4,096 + 0 × 2,048 + 0 × 1,024 + 1 × 512 + 1 × 256 + 1 × 128 + 0 × 64 + 1 × 32 + 0 × 16 + 1 × 8 + 1 × 4 + 1 × 2 + 1 × 1 = 25,519
Octal
6 1 6 5 7
6 × 4,096 + 1 × 512 + 6 × 64 + 5 × 8 + 7 × 1 = 25,519
Hexadecimal
6 3 a f
6 × 4,096 + 3 × 256 + a × 16 + f × 1 = 25,519
Read as powers of two: 16,384 + 8,192 + 512 + 256 + 128 + 32 + 8 + 4 + 2 + 1 = 25,519.
In historical numeral systems
Egyptian
2 fingers, 5 lotuses, 5 coils of rope, 1 hobble, 9 strokes
2 × 10,000 + 5 × 1,000 + 5 × 100 + 1 × 10 + 9 × 1 = 25,519. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
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
Technology & computing
The number in the name of Curve25519 is 25,519. It runs together the exponent and the subtrahend of 2²⁵⁵ − 19, the prime that defines the curve's field. Naming the curve after its own parameters was part of the point: earlier standard curves carried constants nobody could account for.
DocumentedTechnology & computingGeography: worldwide
Common questions
Is 25,519 a prime number?
No, 25,519 is not prime.
What are the factors of 25,519?
The factors of 25,519 are 1, 13, 151, 169, 1963, 25519.
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