21064721 has 4 divisors (see below), whose sum is σ = 21100032. Its totient is φ = 21029412.

The previous prime is 21064679. The next prime is 21064723. The reversal of 21064721 is 12746012.

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 a de Polignac number, because none of the positive numbers 2^k-21064721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21064723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16745 + ... + 17958.

It is an arithmetic number, because the mean of its divisors is an integer number (5275008).

Almost surely, 2^21064721 is an apocalyptic number.

It is an amenable number.

21064721 is a deficient number, since it is larger than the sum of its proper divisors (35311).

21064721 is an equidigital number, since it uses as much as digits as its factorization.

21064721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35310.

The product of its (nonzero) digits is 672, while the sum is 23.

The square root of 21064721 is about 4589.6319024514. The cubic root of 21064721 is about 276.1755560618.

The spelling of 21064721 in words is "twenty-one million, sixty-four thousand, seven hundred twenty-one".