406
406 MHz is the frequency of emergency distress beacons detected by satellite.
- Even
- Composite
Where 406 fits
Why 406 is special
A beacon on this frequency is picked up by an international satellite network and located to within a few kilometres, or metres if it transmits GPS. The system is free at the point of use and has been credited with tens of thousands of rescues.
406 is part of
Factors & digit properties
- Divisors (8)
- 1, 2, 7, 14, 29, 58, 203, 406
- Prime factorisation
- 2 × 7 × 29
- Digit sum
- 10
- Digital root
- 1
Representations
- Decimal
- 406
- Scientific notation
- 4.060 × 10^2
Roman numerals
C D V I
CDVI uses the subtractive pair CD: a hundred before five hundred — five hundred minus a hundred.
Binary
1 1 0 0 1 0 1 1 0
1 × 256 + 1 × 128 + 0 × 64 + 0 × 32 + 1 × 16 + 0 × 8 + 1 × 4 + 1 × 2 + 0 × 1 = 406
Octal
6 2 6
6 × 64 + 2 × 8 + 6 × 1 = 406
Hexadecimal
1 9 6
1 × 256 + 9 × 16 + 6 × 1 = 406
Read as powers of two: 256 + 128 + 16 + 4 + 2 = 406.
In historical numeral systems
Egyptian
4 coils of rope, 6 strokes
4 × 100 + 6 × 1 = 406. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
6 vertical wedges (sixties place), 4 corner wedges + 6 vertical wedges (units place)
6 × 60 + 46 = 406. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
upsilon, then stigma, marked as a numeral
upsilon-stigma + keraia
upsilon + stigma 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 vav
tav-vav
tav (400) + vav (6) = 406, 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
- Deficient number
Related numbers & connections
406 appears in Numbers in radio and communications, the topic covering numbers that carry a documented radio or communications fact.
Two ways of declaring an emergency: a satellite-tracked distress beacon, and a transponder code that tells every radar screen in range. One works anywhere on Earth, the other only where radar reaches.
View 7700 →Technology & computing
406 MHz beacons are tracked by an international satellite system operated jointly by several states, which locates a signal within kilometres anywhere on Earth. The older 121.5 MHz system was switched off in 2009 because it produced too many false alerts to be useful.
DocumentedTechnology & computingGeography: International — Cospas-Sarsat participating states406 MHz distress beacons are processed by the Cospas-Sarsat system and carry a registered identifier, unlike the analogue 121.5 MHz beacons whose satellite monitoring ended in 2009.
DocumentedTechnology & computingGeography: International — Cospas-Sarsat participating statesPeriod: 1982–The frequency used by emergency locator beacons is 406 megahertz (worldwide, COSPAS-SARSAT). Satellite-monitored since 1982, and the only distress frequency the system still processes: the older 121.5 megahertz beacon alerting was switched off in 2009 after decades in which the great majority of its activations were false alarms.
DocumentedTechnology & computingGeography: worldwide, COSPAS-SARSAT
Common questions
Is 406 a prime number?
No, 406 is not prime.
What are the factors of 406?
The factors of 406 are 1, 2, 7, 14, 29, 58, 203, 406.
What is 406 in Roman numerals?
406 in Roman numerals is CDVI. CD is subtractive: a hundred before five hundred — five hundred minus a hundred. Written additively it would be CCCCVI, 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: 3 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026