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|Factorization||2 × 3 × 13|
|Divisors||1, 2, 3, 6, 13, 26, 39, 78|
- the dimension of the exceptional Lie group E6 and several related objects.
- a sphenic number, having 3 distinct prime factors.
- an abundant number with an aliquot sum of 90.
- a semiperfect number, as a multiple of a perfect number.
- the 12th triangular number.
- a palindromic number in bases 5 (3035), 7 (1417), 12 (6612), 25 (3325), 38 (2238), 77 (1177) and all bases greater 78.
- a Harshad number in bases 3, 4, 5, 6, 7, 13 and 14.
- an Erdős–Woods number, since it is possible to find sequences of 78 consecutive integers such that each inner member shares a factor with either the first or the last member.
77 and 78 form a Ruth-Aaron pair.
In other fields
78 is also:
- In reference to gramophone records, 78 refers those meant to be spun at 78 revolutions per minute. Compare: LP, 33 1⁄3 and 45 rpm. 33 + 45 = 78
- A typical tarot deck containing the 21 trump cards, the Fool and the 56 suit cards make up 78 cards
- The total number of gifts in the song The Twelve Days of Christmas (since 78 is the 12th triangular number)
- The Rule of 78s is a method of yearly interest calculation
- The number of the laps of the Monaco Grand Prix since 1985 (with the exception of 1989 by just 77 laps).
- The only non-conforming sequenced episode of the Hello Internet podcast written using the Roman numerals LXXVIII.