• 780 can be written using four 4's:

780 has 24 divisors (see below), whose sum is σ = 2352. Its totient is φ = 192.

The previous prime is 773. The next prime is 787. The reversal of 780 is 87.

780 is a nontrivial binomial coefficient, being equal to C(40, 2).

It is an interprime number because it is at equal distance from previous prime (773) and next prime (787).

It is a Harshad number since it is a multiple of its sum of digits (15).

780 is an undulating number in base 8.

It is a nialpdrome in base 5 and base 12.

It is a zygodrome in base 2.

It is a Saint-Exupery number, since it is equal to the product of the sides of a Pythagorean triangle: 13 × 5 × 12.

It is not an unprimeable number, because it can be changed into a prime (787) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 54 + ... + 66.

It is an arithmetic number, because the mean of its divisors is an integer number (98).

780 is the 39-th triangular number and also the 20-th hexagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1176).

780 is an abundant number, since it is smaller than the sum of its proper divisors (1572).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

780 is a wasteful number, since it uses less digits than its factorization.

780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25 (or 23 counting only the distinct ones).

The product of its (nonzero) digits is 56, while the sum is 15.

The square root of 780 is about 27.9284800875. The cubic root of 780 is about 9.2051640825.

The spelling of 780 in words is "seven hundred eighty", and thus it is an aban number and an oban number.

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