81918399 has 16 divisors (see below), whose sum is σ = 113576960. Its totient is φ = 52462080.

The previous prime is 81918379. The next prime is 81918401. The reversal of 81918399 is 99381918.

It is not a de Polignac number, because 81918399 - 2¹⁶ = 81852863 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 (81918349) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9759 + ... + 16095.

It is an arithmetic number, because the mean of its divisors is an integer number (7098560).

Almost surely, 2^81918399 is an apocalyptic number.

81918399 is a deficient number, since it is larger than the sum of its proper divisors (31658561).

81918399 is a wasteful number, since it uses less digits than its factorization.

81918399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6510.

The product of its digits is 139968, while the sum is 48.

The square root of 81918399 is about 9050.8783551653. The cubic root of 81918399 is about 434.3039893512.

The spelling of 81918399 in words is "eighty-one million, nine hundred eighteen thousand, three hundred ninety-nine".