21013645 has 4 divisors (see below), whose sum is σ = 25216380. Its totient is φ = 16810912.

The previous prime is 21013633. The next prime is 21013709. The reversal of 21013645 is 54631012.

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 14607684 + 6405961 = 3822^2 + 2531^2 .

It is a cyclic number.

It is not a de Polignac number, because 21013645 - 2¹⁷ = 20882573 is a prime.

It is a super-3 number, since 3×21013645³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

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, 2101360 + ... + 2101369.

It is an arithmetic number, because the mean of its divisors is an integer number (6304095).

Almost surely, 2^21013645 is an apocalyptic number.

It is an amenable number.

21013645 is a deficient number, since it is larger than the sum of its proper divisors (4202735).

21013645 is an equidigital number, since it uses as much as digits as its factorization.

21013645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4202734.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21013645 is about 4584.0642447505. The cubic root of 21013645 is about 275.9521594949.

Adding to 21013645 its reverse (54631012), we get a palindrome (75644657).

The spelling of 21013645 in words is "twenty-one million, thirteen thousand, six hundred forty-five".