81821818 has 16 divisors (see below), whose sum is σ = 136732680. Its totient is φ = 36461376.

The previous prime is 81821813. The next prime is 81821827. The reversal of 81821818 is 81812818.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 68840209 + 12981609 = 8297^2 + 3603^2 .

It is not an unprimeable number, because it can be changed into a prime (81821813) 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, 53505 + ... + 55012.

Almost surely, 2^81821818 is an apocalyptic number.

81821818 is a deficient number, since it is larger than the sum of its proper divisors (54910862).

81821818 is a wasteful number, since it uses less digits than its factorization.

81821818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 108561.

The product of its digits is 8192, while the sum is 37.

The square root of 81821818 is about 9045.5413326124. The cubic root of 81821818 is about 434.1332421631.

It can be divided in two parts, 8182 and 1818, that added together give a 4-th power (10000 = 10⁴).

The spelling of 81821818 in words is "eighty-one million, eight hundred twenty-one thousand, eight hundred eighteen".