21001309 has 8 divisors (see below), whose sum is σ = 24090368. Its totient is φ = 17934480.

The previous prime is 21001247. The next prime is 21001319. The reversal of 21001309 is 90310012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21001309 - 2⁷ = 21001181 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21001292 and 21001301.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001319) 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 7 ways as a sum of consecutive naturals, for example, 3477 + ... + 7354.

It is an arithmetic number, because the mean of its divisors is an integer number (3011296).

Almost surely, 2^21001309 is an apocalyptic number.

It is an amenable number.

21001309 is a deficient number, since it is larger than the sum of its proper divisors (3089059).

21001309 is a wasteful number, since it uses less digits than its factorization.

21001309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11115.

The product of its (nonzero) digits is 54, while the sum is 16.

The square root of 21001309 is about 4582.7185163394. The cubic root of 21001309 is about 275.8981499504.

The spelling of 21001309 in words is "twenty-one million, one thousand, three hundred nine".