78391 has 4 divisors (see below), whose sum is σ = 78952. Its totient is φ = 77832.

The previous prime is 78367. The next prime is 78401. The reversal of 78391 is 19387.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 78391 - 2¹¹ = 76343 is a prime.

It is a super-2 number, since 2×78391² = 12290297762, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78301) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 136 + ... + 418.

It is an arithmetic number, because the mean of its divisors is an integer number (19738).

2⁷⁸³⁹¹ is an apocalyptic number.

78391 is a deficient number, since it is larger than the sum of its proper divisors (561).

78391 is a wasteful number, since it uses less digits than its factorization.

78391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 560.

The product of its digits is 1512, while the sum is 28.

The square root of 78391 is about 279.9839281102. The cubic root of 78391 is about 42.7978614240.

It can be divided in two parts, 783 and 91, that multiplied together give a triangular number (71253 = T₃₇₇).

The spelling of 78391 in words is "seventy-eight thousand, three hundred ninety-one".