21009389 has 2 divisors, whose sum is σ = 21009390. Its totient is φ = 21009388.

The previous prime is 21009379. The next prime is 21009403. The reversal of 21009389 is 98390012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13446889 + 7562500 = 3667^2 + 2750^2 .

It is a cyclic number.

It is not a de Polignac number, because 21009389 - 2¹² = 21005293 is a prime.

It is a plaindrome in base 13.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21009379) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504694 + 10504695.

It is an arithmetic number, because the mean of its divisors is an integer number (10504695).

Almost surely, 2^21009389 is an apocalyptic number.

It is an amenable number.

21009389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009389 is an equidigital number, since it uses as much as digits as its factorization.

21009389 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 32.

The square root of 21009389 is about 4583.6000043634. The cubic root of 21009389 is about 275.9335282407.

The spelling of 21009389 in words is "twenty-one million, nine thousand, three hundred eighty-nine".