21331218 has 16 divisors (see below), whose sum is σ = 42971040. Its totient is φ = 7058976.

The previous prime is 21331217. The next prime is 21331267. The reversal of 21331218 is 81213312.

It is a super-2 number, since 2×21331218² = 910041722727048, which contains 22 as substring.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21331194 and 21331203.

It is not an unprimeable number, because it can be changed into a prime (21331217) 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, 11955 + ... + 13622.

It is an arithmetic number, because the mean of its divisors is an integer number (2685690).

Almost surely, 2^21331218 is an apocalyptic number.

21331218 is an abundant number, since it is smaller than the sum of its proper divisors (21639822).

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

21331218 is a wasteful number, since it uses less digits than its factorization.

21331218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25721.

The product of its digits is 288, while the sum is 21.

The square root of 21331218 is about 4618.5731562897. The cubic root of 21331218 is about 277.3353426234.

The spelling of 21331218 in words is "twenty-one million, three hundred thirty-one thousand, two hundred eighteen".