81813887 has 4 divisors (see below), whose sum is σ = 83554656. Its totient is φ = 80073120.

The previous prime is 81813883. The next prime is 81813899. The reversal of 81813887 is 78831818.

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 81813887 - 2² = 81813883 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81813881) 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, 870314 + ... + 870407.

It is an arithmetic number, because the mean of its divisors is an integer number (20888664).

Almost surely, 2^81813887 is an apocalyptic number.

81813887 is a deficient number, since it is larger than the sum of its proper divisors (1740769).

81813887 is a wasteful number, since it uses less digits than its factorization.

81813887 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1740768.

The product of its digits is 86016, while the sum is 44.

The square root of 81813887 is about 9045.1029292098. The cubic root of 81813887 is about 434.1192148450.

The spelling of 81813887 in words is "eighty-one million, eight hundred thirteen thousand, eight hundred eighty-seven".