21211218 has 36 divisors (see below), whose sum is σ = 53463150. Its totient is φ = 6060096.

The previous prime is 21211217. The next prime is 21211237. The reversal of 21211218 is 81211212.

It can be written as a sum of positive squares in only one way, i.e., 18173169 + 3038049 = 4263^2 + 1743^2 .

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a self number, because there is not a number n which added to its sum of digits gives 21211218.

It is not an unprimeable number, because it can be changed into a prime (21211217) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 11143 + ... + 12906.

Almost surely, 2^21211218 is an apocalyptic number.

21211218 is an abundant number, since it is smaller than the sum of its proper divisors (32251932).

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

21211218 is a wasteful number, since it uses less digits than its factorization.

21211218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24071 (or 24061 counting only the distinct ones).

The product of its digits is 64, while the sum is 18.

The square root of 21211218 is about 4605.5638091335. The cubic root of 21211218 is about 276.8143090295.

The spelling of 21211218 in words is "twenty-one million, two hundred eleven thousand, two hundred eighteen".