21628309 has 4 divisors (see below), whose sum is σ = 21644704. Its totient is φ = 21611916.

The previous prime is 21628283. The next prime is 21628339. The reversal of 21628309 is 90382612.

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 21628309 - 2¹³ = 21620117 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21628339) 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, 6027 + ... + 8920.

It is an arithmetic number, because the mean of its divisors is an integer number (5411176).

Almost surely, 2^21628309 is an apocalyptic number.

It is an amenable number.

21628309 is a deficient number, since it is larger than the sum of its proper divisors (16395).

21628309 is a wasteful number, since it uses less digits than its factorization.

21628309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16394.

The product of its (nonzero) digits is 5184, while the sum is 31.

The square root of 21628309 is about 4650.6245817094. The cubic root of 21628309 is about 278.6169424022.

The spelling of 21628309 in words is "twenty-one million, six hundred twenty-eight thousand, three hundred nine".