Number reference
78 explained.
78: seventy-eight, composite, triangular number; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- seventy-eight
- Classification
- composite
- Factors
- 1, 2, 3, 6, 13, 26, 39, 78
- Prime factorization
- 2 × 3 × 13
- Square root
- 8.831761
- Cube root
- 4.272659
- Binary
- 1001110
- Octal
- 116
- Hexadecimal
- 4E
- Roman numeral
- LXXVIII
- Digit sum
- 15
- Digital root
- 6
What makes 78 notable
- Triangular number. 78 is the 12th triangular number: it is the sum 1 + 2 + … + 12, the count of items in a triangle with 12 rows.
78 in everyday use
Seventy-eight is the atomic number of platinum, the precious metal of catalytic converters and the benchmark for a "platinum" record or anniversary. Shellac gramophone records spun at 78 revolutions per minute from the 1920s until vinyl LPs and 45s replaced them. A full tarot deck has 78 cards: 22 major arcana and 56 minor. Adding up every gift in "The Twelve Days of Christmas" on the twelfth day alone gives 78.
Seventy-eight is the twelfth triangular number, 1 + 2 + … + 12, which is exactly why the twelfth day of Christmas brings 78 gifts. It is a sphenic number, 2 × 3 × 13, with eight divisors, and its proper divisors sum to 90, so it is abundant. It is also the number of ways to choose two items from thirteen. In binary it is 1001110.
Nearby numbers
How to read this page
The factor list shows every way 78 splits into equal whole-number groups — 8 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 78 for contexts that do not use decimal.
Percentage calculator · Fraction calculator · Browse Number Explorer