81870391 has 4 divisors (see below), whose sum is σ = 82282000. Its totient is φ = 81458784.

The previous prime is 81870389. The next prime is 81870413. The reversal of 81870391 is 19307818.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81870391 - 2¹ = 81870389 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81870391.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81870311) 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, 205506 + ... + 205903.

It is an arithmetic number, because the mean of its divisors is an integer number (20570500).

Almost surely, 2^81870391 is an apocalyptic number.

81870391 is a deficient number, since it is larger than the sum of its proper divisors (411609).

81870391 is a wasteful number, since it uses less digits than its factorization.

81870391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 411608.

The product of its (nonzero) digits is 12096, while the sum is 37.

The square root of 81870391 is about 9048.2258481981. The cubic root of 81870391 is about 434.2191319788.

The spelling of 81870391 in words is "eighty-one million, eight hundred seventy thousand, three hundred ninety-one".