66
Route 66 ran from Chicago to Santa Monica and was decommissioned in 1985, though the number long outlived the road. 66 is the eleventh triangular number, and the atomic number of dysprosium.
- Even
- Composite
Where 66 fits
Why 66 is special
66's cultural fame comes from Route 66, the storied Chicago-to-Santa-Monica highway (1926-1985) that remains a symbol of mid-20th-century American road culture.
Same number, different meanings
How 66 is understood across different contexts — never implying one meaning because of another.
- Mathematics
66's cultural fame comes from Route 66, the storied Chicago-to-Santa-Monica highway (1926-1985) that remains a symbol of mid-20th-century American road culture.
- History
US Route 66, established in 1926 and mostly decommissioned by 1985, was a historic highway running from Chicago to Santa Monica, California, and remains a strong symbol of mid-20th-century American road culture.
- Culture
US Route 66 was decommissioned in 1985 and removed from the highway system, and the number remained a cultural reference through music, television and tourism. Sections survive as state and local roads signed as historic.
- Science
66 is the atomic number of dysprosium. Added to neodymium magnets it lets them keep working when hot, which matters in wind-turbine generators and electric-vehicle motors.
Factors & digit properties
- Divisors (8)
- 1, 2, 3, 6, 11, 22, 33, 66
- Prime factorisation
- 2 × 3 × 11
- Digit sum
- 12
- Digital root
- 3
Representations
- Decimal
- 66
- Scientific notation
- 6.600 × 10^1
Roman numerals
L X V I
Binary
1 0 0 0 0 1 0
1 × 64 + 0 × 32 + 0 × 16 + 0 × 8 + 0 × 4 + 1 × 2 + 0 × 1 = 66
Octal
1 0 2
1 × 64 + 0 × 8 + 2 × 1 = 66
Hexadecimal
4 2
4 × 16 + 2 × 1 = 66
Read as powers of two: 64 + 2 = 66.
In historical numeral systems
Egyptian
6 hobbles, 6 strokes
6 × 10 + 6 × 1 = 66. The signs are simply repeated and added; where they sit on the line is a matter of layout, not value.
Babylonian
1 vertical wedge (sixties place), 6 vertical wedges (units place)
1 × 60 + 6 = 66. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
xi, then stigma, marked as a numeral
xi-stigma + keraia
xi + stigma written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
samekh, then vav
samekh-vav
samekh (60) + vav (6) = 66, written in descending order.
Chinese numerals
liù shí liù
liù shí liù
六 before 十 multiplies it: 6 tens. 六 after it adds 6. The written form mirrors the arithmetic — "liù shí liù". The financial (anti-fraud) form is 陸拾陸.
Maya
3 dots (upper, twenties place) over 1 bar + 1 dot (lower, units place)
3 × 20 + 6 = 66. Places stack vertically with the smallest at the bottom, so the upper group is worth twenty times the lower.
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
- Palindromic number
- Abundant number
- Repdigit
- Hexagonal number
Related numbers & connections
33 is a factor of 66 (33 × 2 = 66).
View 33 →67 and 66 are consecutive integers.
View 67 →US Route 66 was decommissioned in 1985 and the number outlived the road it designated.
History
US Route 66, established in 1926 and mostly decommissioned by 1985, was a historic highway running from Chicago to Santa Monica, California, and remains a strong symbol of mid-20th-century American road culture.
DocumentedHistoryGeography: United StatesPeriod: 1926-1985
Culture
US Route 66 was decommissioned in 1985 and removed from the highway system, and the number remained a cultural reference through music, television and tourism. Sections survive as state and local roads signed as historic.
DocumentedCultureGeography: United StatesPeriod: 1926–1985
Mathematics
66 is the eleventh triangular number: 1 + 2 + … + 11. It is therefore the number of handshakes in a room of twelve people, since each of the twelve greets eleven others and every handshake is counted twice.
DocumentedMathematics
Science
66 is the atomic number of dysprosium. Added to neodymium magnets it lets them keep working when hot, which matters in wind-turbine generators and electric-vehicle motors.
DocumentedScience
Common questions
Does Route 66 still exist?
Not as a US highway. It was decommissioned in 1985 after the interstates that replaced it were completed, and the shields came down. Long stretches survive as state and local roads, many signed as Historic Route 66, and the number has kept a cultural life through music, television and tourism that the road itself no longer has.
Is 66 a prime number?
No, 66 is not prime.
What are the factors of 66?
The factors of 66 are 1, 2, 3, 6, 11, 22, 33, 66.
What is 66 in Roman numerals?
66 in Roman numerals is LXVI.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 4 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026