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|Factorization||7 × 11|
|Divisors||1, 7, 11, 77|
- the 22nd discrete biprime and the first of the (7.q) family.
- a Blum integer since both 7 and 11 are Gaussian primes.
- the sum of three consecutive squares, 42 + 52 + 62.
- the sum of the first eight prime numbers.
- the number of integer partitions of the number 12.
- the largest number that cannot be written as a sum of distinct numbers whose reciprocals sum to 1.
- the number of digits of the 12th perfect number.
It and its sibling 49 are the only 2-digit numbers whose home primes (in base 10) have not been calculated.
During World War II in Sweden at the border with Norway, "77" was used as a shibboleth (password), because the tricky pronunciation in Swedish made it easy to instantly discern whether the speaker was native Swedish, Norwegian, or German.
In the Islamic tradition, "77" figures prominently. Muhammad is reported to have explained, "Faith has sixty-odd, or seventy-odd branches, the highest and best of which is to declare that there is no god but God, and the lowest of which is to remove something harmful from a road. Shyness, too, is a branch of faith." While some scholars refrain from clarifying "sixty-odd or seventy-odd", various numbers have been suggested, 77 being the most common. Some have gone so far as to delineate these branches.
In religious numerology
In certain numerological systems based on the English alphabet, the number 77 is associated with Jesus Christ. CHRIST is C = 3, H = 8, R = 18, I = 9, S = 19, T = 20, which added together equal 77.
'Liber 77' is the gematrian name for Liber OZ- a brief but popular publication by Aliester Crowley. The word 'oz', which means 'strength', is composed of two hebrew letters- ayin and zayin, which have gematrian values of 70 and 7 respectively, thus adding up to 77.
In other fields
Seventy-seven is also:
- 10-77 – the New York City Fire Department's (FDNY) 10 code for high-rise, multiple-dwelling fire 
- Shortening of a 1950s-60s TV series, 77 Sunset Strip
- Group of 77, a group of developing nations at the United Nations
- 77 – Talking Heads's debut album (Talking Heads: 77) released in 1977
- The 77's, an American Rock band
- The temperature, in Fahrenheit, some characteristics of semiconductors are specifically given in a datasheet (77 °F = 25 °C).
- Sloane, N.J.A. (ed.). "Sequence A016105 (Blum integers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-29.
- Sloane, N.J.A. (ed.). "Sequence A000041". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- "What's Special About This Number?".
- Caldwell, Chris K. "Mersenne Primes: History, Theorems and Lists".
- The Science behind Sudoku, J.P. Delahaye
- Buchan, Jamie (2010), Easy as Pi: The Countless Ways We Use Numbers Every Day, Penguin, ISBN 9781606522783.
- A Verdict of Mufti Muhammad Hassan
- "Imam al-Tahanawi on the Seventy-Seven Branches".
- "The genealogy of Jesus".
- "10 Codes".
Media related to 77 (number) at Wikimedia Commons