78 (number) facts for kids

78 (seventy-eight) is a natural number. It comes right after seventy-seven and before seventy-nine. It is also an even number.

Fun Facts About 78

78 in Mathematics

• 78 is a sphenic number. This means it has three different prime numbers that multiply together to make it. For 78, these are 2, 3, and 13 (2 × 3 × 13 = 78).
• It is an abundant number. If you add up all its divisors (numbers that divide into it evenly, not including 78 itself), the sum is greater than 78. The divisors of 78 are 1, 2, 3, 6, 13, 26, 39. Their sum is 1 + 2 + 3 + 6 + 13 + 26 + 39 = 90, which is more than 78.
• 78 is a semiperfect number. This means you can add up some of its divisors to get 78. For example, 2 + 6 + 13 + 26 + 31 = 78.
• It is the 12th triangular number. A triangular number is the sum of all whole numbers up to a certain number. So, 1 + 2 + 3 + ... + 12 = 78.
• 78 is a palindromic number in some number systems (called "bases"). A palindromic number reads the same forwards and backwards. For example, in base 5, 78 is written as 303. In base 7, it's 141.
• It is a Harshad number in several bases. A Harshad number can be divided by the sum of its digits in that base.
• 77 and 78 form a Ruth-Aaron pair. This means that if you add up the prime factors of 77 (7 + 11 = 18) and the prime factors of 78 (2 + 3 + 13 = 18), both sums are the same.

78 in Science

• 78 is the atomic number of platinum. Platinum is a rare and valuable metal. It is known for being very resistant to corrosion.

78 in Other Areas

• When people talk about old gramophone records, 78 refers to records that spin at 78 revolutions per minute (rpm). These were common before LPs (which spin at 33+1⁄3 rpm) and 45 rpm records became popular.
• A typical tarot deck has 78 cards. This includes 21 special "trump" cards, one "Fool" card, and 56 suit cards.
• The Rule of 78s is a way to calculate interest on a loan. It's often used for loans that are paid back early.

See also

In Spanish: Setenta y ocho para niños