21045545 has 4 divisors (see below), whose sum is σ = 25254660. Its totient is φ = 16836432.

The previous prime is 21045539. The next prime is 21045547. The reversal of 21045545 is 54554012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14160169 + 6885376 = 3763^2 + 2624^2 .

It is a cyclic number.

It is not a de Polignac number, because 21045545 - 2⁶ = 21045481 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21045547) 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, 2104550 + ... + 2104559.

It is an arithmetic number, because the mean of its divisors is an integer number (6313665).

Almost surely, 2^21045545 is an apocalyptic number.

It is an amenable number.

21045545 is a deficient number, since it is larger than the sum of its proper divisors (4209115).

21045545 is an equidigital number, since it uses as much as digits as its factorization.

21045545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4209114.

The product of its (nonzero) digits is 4000, while the sum is 26.

The square root of 21045545 is about 4587.5423703765. The cubic root of 21045545 is about 276.0917263209.

Adding to 21045545 its reverse (54554012), we get a palindrome (75599557).

The spelling of 21045545 in words is "twenty-one million, forty-five thousand, five hundred forty-five".