81918687 has 8 divisors (see below), whose sum is σ = 109305904. Its totient is φ = 54571968.

The previous prime is 81918679. The next prime is 81918691. The reversal of 81918687 is 78681918.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81918687 - 2³ = 81918679 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 (81918637) 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, 5038 + ... + 13755.

It is an arithmetic number, because the mean of its divisors is an integer number (13663238).

Almost surely, 2^81918687 is an apocalyptic number.

81918687 is a deficient number, since it is larger than the sum of its proper divisors (27387217).

81918687 is a wasteful number, since it uses less digits than its factorization.

81918687 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20249.

The product of its digits is 193536, while the sum is 48.

The square root of 81918687 is about 9050.8942652094. The cubic root of 81918687 is about 434.3044983105.

The spelling of 81918687 in words is "eighty-one million, nine hundred eighteen thousand, six hundred eighty-seven".