77 (number)
From Halbeeg, the open encyclopedia · Af-Soomaali
78 languages
77 is a natural number that comes after 76 and before 78. It is a composite number, meaning it has divisors other than 1 and itself. Its Roman numeral form is LXXVII, and in binary it is written 1001101.
Like all two-digit numbers with identical digits, 77 is a palindrome when written in base ten—it reads the same forwards and backwards.
Mathematical properties
77 equals 7 × 11. Since both are prime numbers, 77 is classified as a semiprime—the product of exactly two primes. Its divisors are 1, 7, 11, and 77; their sum is 96. The sum of its digits (7 + 7) is 14.
Another notable property: 77 is the sum of the first eight primes (2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 = 77). It can also be expressed as the sum of three perfect squares, for example 4 + 9 + 64 = 77.
Language and numeration
In Somali, 77 is named "toddobaatan iyo toddoba" (seventy and seven). Somali numeration follows a base-ten system: after the tens place (toddobaatan) comes the ones place (toddoba), linked by the conjunction "iyo" (and).
Other uses
77 is the atomic number of iridium (Ir) on the periodic table. The number also appears in the names of organizations and groups, such as the Group of 77, a coalition of developing countries that cooperates within the United Nations, named after the number of countries that signed its founding charter.