77
77 is the atomic number of iridium, which is far commoner in asteroids than in Earth's crust. A worldwide iridium-rich rock layer is central evidence that an asteroid impact ended the age of the dinosaurs.
- Odd
- Composite
Where 77 fits
Why 77 is special
77's element connects a rare metal to one of the most consequential events in Earth's history, dated to about 66 million years ago.
Same number, different meanings
How 77 is understood across different contexts — never implying one meaning because of another.
- Mathematics
77's element connects a rare metal to one of the most consequential events in Earth's history, dated to about 66 million years ago.
- History
A thin, unusually iridium-rich layer found in rock worldwide, dating to about 66 million years ago, is central evidence for the asteroid-impact explanation of the mass extinction that ended the age of dinosaurs.
- Science
77 is the atomic number of iridium, among the densest and most corrosion-resistant elements. It is far commoner in asteroids than in Earth's crust — a difference that turned out to matter a great deal.
77 is part of
Factors & digit properties
- Divisors (4)
- 1, 7, 11, 77
- Prime factorisation
- 7 × 11
- Digit sum
- 14
- Digital root
- 5
Representations
- Decimal
- 77
- Scientific notation
- 7.700 × 10^1
Roman numerals
L X X V I I
Binary
1 0 0 1 1 0 1
1 × 64 + 0 × 32 + 0 × 16 + 1 × 8 + 1 × 4 + 0 × 2 + 1 × 1 = 77
Octal
1 1 5
1 × 64 + 1 × 8 + 5 × 1 = 77
Hexadecimal
4 d
4 × 16 + d × 1 = 77
Read as powers of two: 64 + 8 + 4 + 1 = 77.
In historical numeral systems
Egyptian
7 hobbles, 7 strokes
7 × 10 + 7 × 1 = 77. 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), 1 corner wedge + 7 vertical wedges (units place)
1 × 60 + 17 = 77. Places are separated by a space on the tablet, with the higher place written first.
Greek (Ionic)
omicron, then zeta, marked as a numeral
omicron-zeta + keraia
omicron + zeta written in descending order and added — the letters carry their values wherever they stand, so this is addition, not place value.
Hebrew numerals
ayin, then zayin
ayin-zayin
ayin (70) + zayin (7) = 77, written in descending order.
Chinese numerals
qī shí qī
qī shí qī
七 before 十 multiplies it: 7 tens. 七 after it adds 7. The written form mirrors the arithmetic — "qī shí qī". The financial (anti-fraud) form is 柒拾柒.
Maya
3 dots (upper, twenties place) over 3 bars + 2 dots (lower, units place)
3 × 20 + 17 = 77. 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
- Palindromic number
- Deficient number
- Repdigit
- Semiprime
Related numbers & connections
11 is a factor of 77 (11 × 7 = 77).
View 11 →Mathematically related
- has factor11
why?
Strength 0.50, confidence "high".
History
A thin, unusually iridium-rich layer found in rock worldwide, dating to about 66 million years ago, is central evidence for the asteroid-impact explanation of the mass extinction that ended the age of dinosaurs.
DocumentedHistory
Science
77 is the atomic number of iridium, among the densest and most corrosion-resistant elements. It is far commoner in asteroids than in Earth's crust — a difference that turned out to matter a great deal.
DocumentedScience
Common questions
Is 77 a prime number?
No, 77 is not prime.
What are the factors of 77?
The factors of 77 are 1, 7, 11, 77.
What is 77 in Roman numerals?
77 in Roman numerals is LXXVII.
About this page's data
Mathematical facts:computed directly from the number's value — nothing to source or verify externally.
Contextual records: 2 reviewer-confirmed records, sourced and reviewed before publication.
Last reviewed: 15 July 2026