81987818 has 16 divisors (see below), whose sum is σ = 136054080. Its totient is φ = 36741600.

The previous prime is 81987817. The next prime is 81987853. The reversal of 81987818 is 81878918.

It is a super-2 number, since 2×81987818² = 13444004600802248, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81987811) 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, 24683 + ... + 27806.

It is an arithmetic number, because the mean of its divisors is an integer number (8503380).

Almost surely, 2^81987818 is an apocalyptic number.

81987818 is a deficient number, since it is larger than the sum of its proper divisors (54066262).

81987818 is a wasteful number, since it uses less digits than its factorization.

81987818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52573.

The product of its digits is 258048, while the sum is 50.

The square root of 81987818 is about 9054.7124747283. The cubic root of 81987818 is about 434.4266334978.

Subtracting from 81987818 its reverse (81878918), we obtain a square (108900 = 330²).

The spelling of 81987818 in words is "eighty-one million, nine hundred eighty-seven thousand, eight hundred eighteen".