21305009 has 4 divisors (see below), whose sum is σ = 23241840. Its totient is φ = 19368180.

The previous prime is 21305003. The next prime is 21305027. The reversal of 21305009 is 90050312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21305009 - 2⁸ = 21304753 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21305003) 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, 968399 + ... + 968420.

It is an arithmetic number, because the mean of its divisors is an integer number (5810460).

Almost surely, 2^21305009 is an apocalyptic number.

It is an amenable number.

21305009 is a deficient number, since it is larger than the sum of its proper divisors (1936831).

21305009 is a wasteful number, since it uses less digits than its factorization.

21305009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1936830.

The product of its (nonzero) digits is 270, while the sum is 20.

The square root of 21305009 is about 4615.7349360638. The cubic root of 21305009 is about 277.2217116536.

The spelling of 21305009 in words is "twenty-one million, three hundred five thousand, nine".