21669721 has 4 divisors (see below), whose sum is σ = 22173712. Its totient is φ = 21165732.

The previous prime is 21669719. The next prime is 21669727. The reversal of 21669721 is 12796612.

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 21669721 - 2¹ = 21669719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21669727) 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 3 ways as a sum of consecutive naturals, for example, 251931 + ... + 252016.

It is an arithmetic number, because the mean of its divisors is an integer number (5543428).

Almost surely, 2^21669721 is an apocalyptic number.

It is an amenable number.

21669721 is a deficient number, since it is larger than the sum of its proper divisors (503991).

21669721 is an equidigital number, since it uses as much as digits as its factorization.

21669721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 503990.

The product of its digits is 9072, while the sum is 34.

The square root of 21669721 is about 4655.0747577241. The cubic root of 21669721 is about 278.7946528372.

The spelling of 21669721 in words is "twenty-one million, six hundred sixty-nine thousand, seven hundred twenty-one".