21040645 has 12 divisors (see below), whose sum is σ = 26823204. Its totient is φ = 15841280.

The previous prime is 21040633. The next prime is 21040651. The reversal of 21040645 is 54604012.

It can be written as a sum of positive squares in 6 ways, for example, as 3992004 + 17048641 = 1998^2 + 4129^2 .

It is not a de Polignac number, because 21040645 - 2⁷ = 21040517 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5836 + ... + 8725.

It is an arithmetic number, because the mean of its divisors is an integer number (2235267).

Almost surely, 2^21040645 is an apocalyptic number.

It is an amenable number.

21040645 is a deficient number, since it is larger than the sum of its proper divisors (5782559).

21040645 is a wasteful number, since it uses less digits than its factorization.

21040645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14600 (or 14583 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 22.

The square root of 21040645 is about 4587.0082842742. The cubic root of 21040645 is about 276.0702973286.

Adding to 21040645 its reverse (54604012), we get a palindrome (75644657).

The spelling of 21040645 in words is "twenty-one million, forty thousand, six hundred forty-five".