21025945 has 4 divisors (see below), whose sum is σ = 25231140. Its totient is φ = 16820752.

The previous prime is 21025937. The next prime is 21025981. The reversal of 21025945 is 54952012.

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 13424896 + 7601049 = 3664^2 + 2757^2 .

It is a cyclic number.

It is not a de Polignac number, because 21025945 - 2³ = 21025937 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2102590 + ... + 2102599.

It is an arithmetic number, because the mean of its divisors is an integer number (6307785).

Almost surely, 2^21025945 is an apocalyptic number.

It is an amenable number.

21025945 is a deficient number, since it is larger than the sum of its proper divisors (4205195).

21025945 is an equidigital number, since it uses as much as digits as its factorization.

21025945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4205194.

The product of its (nonzero) digits is 3600, while the sum is 28.

The square root of 21025945 is about 4585.4056527204. The cubic root of 21025945 is about 276.0059903832.

Adding to 21025945 its reverse (54952012), we get a palindrome (75977957).

The spelling of 21025945 in words is "twenty-one million, twenty-five thousand, nine hundred forty-five".