21045556 has 12 divisors (see below), whose sum is σ = 42091168. Its totient is φ = 9019512.

The previous prime is 21045553. The next prime is 21045593. The reversal of 21045556 is 65554012.

21045556 is nontrivially palindromic in base 15.

21045556 is an admirable number.

It is a Harshad number since it is a multiple of its sum of digits (28), and also a Moran number because the ratio is a prime number: 751627 = 21045556 / (2 + 1 + 0 + 4 + 5 + 5 + 5 + 6).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21045553) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 375786 + ... + 375841.

Almost surely, 2^21045556 is an apocalyptic number.

It is an amenable number.

21045556 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21045556 is a wasteful number, since it uses less digits than its factorization.

21045556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 751638 (or 751636 counting only the distinct ones).

The product of its (nonzero) digits is 6000, while the sum is 28.

The square root of 21045556 is about 4587.5435692754. The cubic root of 21045556 is about 276.0917744231.

Adding to 21045556 its reverse (65554012), we get a palindrome (86599568).

The spelling of 21045556 in words is "twenty-one million, forty-five thousand, five hundred fifty-six".