Number reference
77 explained.
77: seventy-seven, composite, repdigit; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- seventy-seven
- Classification
- composite
- Factors
- 1, 7, 11, 77
- Prime factorization
- 7 × 11
- Square root
- 8.774964
- Cube root
- 4.254321
- Binary
- 1001101
- Octal
- 115
- Hexadecimal
- 4D
- Roman numeral
- LXXVII
- Digit sum
- 14
- Digital root
- 5
What makes 77 notable
- Repdigit. 77 is written with a single repeated digit, so it is divisible by the repunit of the same length.
77 in everyday use
Seventy-seven is the atomic number of iridium, the metal whose worldwide layer in sediment first pointed to the asteroid impact that ended the dinosaurs. The Boeing 777 is the world's largest twin-engine jetliner, and 77 Sunset Strip was a television detective series of the late 1950s. In American football, 77 was the jersey number of Red Grange, the "Galloping Ghost" of the 1920s, and the Chicago Bears retired it in his honour.
Seventy-seven is 7 × 11 and the sum of the first eight primes, 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19. It is also the sum of three consecutive squares, 16 + 25 + 36. It is the smallest number with multiplicative persistence 4: multiplying its digits gives 49, then 36, then 18, then 8 — four steps before a single digit. In binary it is 1001101.
Nearby numbers
How to read this page
The factor list shows every way 77 splits into equal whole-number groups — 4 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 77 for contexts that do not use decimal.
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