21211818 has 64 divisors (see below), whose sum is σ = 47589120. Its totient is φ = 6272000.

The previous prime is 21211811. The next prime is 21211823. The reversal of 21211818 is 81811212.

It is not an unprimeable number, because it can be changed into a prime (21211811) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 209968 + ... + 210068.

It is an arithmetic number, because the mean of its divisors is an integer number (743580).

Almost surely, 2^21211818 is an apocalyptic number.

21211818 is an abundant number, since it is smaller than the sum of its proper divisors (26377302).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21211818 is a wasteful number, since it uses less digits than its factorization.

21211818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 223.

The product of its digits is 256, while the sum is 24.

The square root of 21211818 is about 4605.6289472775. The cubic root of 21211818 is about 276.8169190795.

The spelling of 21211818 in words is "twenty-one million, two hundred eleven thousand, eight hundred eighteen".