81931618 has 4 divisors (see below), whose sum is σ = 122897430. Its totient is φ = 40965808.

The previous prime is 81931573. The next prime is 81931631. The reversal of 81931618 is 81613918.

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

It can be written as a sum of positive squares in only one way, i.e., 81486729 + 444889 = 9027^2 + 667^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20482903 + ... + 20482906.

Almost surely, 2^81931618 is an apocalyptic number.

81931618 is a deficient number, since it is larger than the sum of its proper divisors (40965812).

81931618 is a wasteful number, since it uses less digits than its factorization.

81931618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40965811.

The product of its digits is 10368, while the sum is 37.

The square root of 81931618 is about 9051.6085863232. The cubic root of 81931618 is about 434.3273490023.

The spelling of 81931618 in words is "eighty-one million, nine hundred thirty-one thousand, six hundred eighteen".