78 (number) facts for kids

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 ← 77 78 79 →
Cardinal seventy-eight
Ordinal 78th
(seventy-eighth)
Factorization 2 × 3 × 13
Divisors 1, 2, 3, 6, 13, 26, 39, 78
Greek numeral ΟΗ´
Roman numeral LXXVIII
Binary 10011102
Ternary 22203
Senary 2106
Octal 1168
Duodecimal 6612

78 (seventy-eight) is the natural number. It comes between seventy-seven and seventy-nine, and is an even number.

In mathematics

78 is:

• 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), and 38 (2238).
• 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, 3313 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 Rule of 78s is a method of yearly interest calculation