21005118 has 48 divisors (see below), whose sum is σ = 48016800. Its totient is φ = 6623232.

The previous prime is 21005111. The next prime is 21005123. The reversal of 21005118 is 81150012.

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

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21005118.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005111) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 46558 + ... + 47006.

It is an arithmetic number, because the mean of its divisors is an integer number (1000350).

Almost surely, 2^21005118 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21005118, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24008400).

21005118 is an abundant number, since it is smaller than the sum of its proper divisors (27011682).

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

21005118 is a wasteful number, since it uses less digits than its factorization.

21005118 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 593 (or 590 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 18.

The square root of 21005118 is about 4583.1340805174. The cubic root of 21005118 is about 275.9148287921.

The spelling of 21005118 in words is "twenty-one million, five thousand, one hundred eighteen".