21398909 has 8 divisors (see below), whose sum is σ = 24917760. Its totient is φ = 17995536.

The previous prime is 21398899. The next prime is 21398917. The reversal of 21398909 is 90989312.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21398909 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21398999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28469 + ... + 29210.

It is an arithmetic number, because the mean of its divisors is an integer number (3114720).

Almost surely, 2^21398909 is an apocalyptic number.

It is an amenable number.

21398909 is a deficient number, since it is larger than the sum of its proper divisors (3518851).

21398909 is an equidigital number, since it uses as much as digits as its factorization.

21398909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57739.

The product of its (nonzero) digits is 34992, while the sum is 41.

The square root of 21398909 is about 4625.8954808772. The cubic root of 21398909 is about 277.6283917413.

The spelling of 21398909 in words is "twenty-one million, three hundred ninety-eight thousand, nine hundred nine".