990
Port 990 carries FTPS — FTP wrapped in TLS.
- Even
- Composite
Where 990 fits
Why 990 is special
990 encrypts the control channel that plain FTP sends in clear text, passwords included. It is distinct from SFTP, which is unrelated and runs over SSH on port 22 — a naming collision that causes genuine configuration errors.
990 is part of
Factors & digit properties
- Divisors (24)
- 1, 2, 3, 5, 6, 9, 10, 11, 15, 18, 22, 30, 33, 45, 55, 66, 90, 99, 110, 165, 198, 330, 495, 990
- Prime factorisation
- 2 × 3^2 × 5 × 11
- Digit sum
- 18
- Digital root
- 9
Representations
- Decimal
- 990
- Scientific notation
- 9.900 × 10^2
Roman numerals
C M X C
CMXC uses the subtractive pair XC: ten before a hundred — a hundred minus ten.
Binary
1 1 1 1 0 1 1 1 1 0
1 × 512 + 1 × 256 + 1 × 128 + 1 × 64 + 0 × 32 + 1 × 16 + 1 × 8 + 1 × 4 + 1 × 2 + 0 × 1 = 990
Octal
1 7 3 6
1 × 512 + 7 × 64 + 3 × 8 + 6 × 1 = 990
Hexadecimal
3 d e
3 × 256 + d × 16 + e × 1 = 990
Read as powers of two: 512 + 256 + 128 + 64 + 16 + 8 + 4 + 2 = 990.
In historical numeral systems
Egyptian
9 coils of rope, 9 hobbles
9 × 100 + 9 × 10 = 990. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 corner wedge + 6 vertical wedges (sixties place), 3 corner wedges (units place)
16 × 60 + 30 = 990. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
sampi, then koppa, marked as a numeral
sampi-koppa + keraia
sampi + koppa 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 qof, then tsadi
tav-tav-qof-tsadi
tav (400) + tav (400) + qof (100) + tsadi (90) = 990, 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
- Triangular number
- Abundant number
- Harshad (Niven) number
Related numbers & connections
Plain FTP sends credentials in clear text on port 21; FTPS wraps the same protocol in TLS on 990. Neither is SFTP, which shares no code with either and runs over SSH.
View 21 →Other connections
- contrasts with21
why?
Strength 0.50, confidence "high".
Technology & computing
FTPS is FTP wrapped in TLS on port 990. SFTP is a completely different protocol running over SSH on port 22. The names differ by one letter and share no code, which causes real configuration errors rather than merely pedantic ones.
DocumentedTechnology & computing
Common questions
Is 990 a prime number?
No, 990 is not prime.
What are the factors of 990?
The factors of 990 are 1, 2, 3, 5, 6, 9, 10, 11, 15, 18, 22, 30, 33, 45, 55, 66, 90, 99, 110, 165, 198, 330, 495, 990.
What is 990 in Roman numerals?
990 in Roman numerals is CMXC. XC is subtractive: ten before a hundred — a hundred minus ten. Written additively it would be DCCCCLXXXX, which Roman inscriptions used freely — the strict subtractive form is a later convention.
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