21013309 has 4 divisors (see below), whose sum is σ = 22249404. Its totient is φ = 19777216.

The previous prime is 21013303. The next prime is 21013357. The reversal of 21013309 is 90331012.

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 17222500 + 3790809 = 4150^2 + 1947^2 .

It is a cyclic number.

It is not a de Polignac number, because 21013309 - 2³ = 21013301 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21013301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 618022 + ... + 618055.

It is an arithmetic number, because the mean of its divisors is an integer number (5562351).

Almost surely, 2^21013309 is an apocalyptic number.

It is an amenable number.

21013309 is a deficient number, since it is larger than the sum of its proper divisors (1236095).

21013309 is a wasteful number, since it uses less digits than its factorization.

21013309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1236094.

The product of its (nonzero) digits is 162, while the sum is 19.

The square root of 21013309 is about 4584.0275959030. The cubic root of 21013309 is about 275.9506886979.

The spelling of 21013309 in words is "twenty-one million, thirteen thousand, three hundred nine".