21523309 has 4 divisors (see below), whose sum is σ = 22789404. Its totient is φ = 20257216.

The previous prime is 21523283. The next prime is 21523339. The reversal of 21523309 is 90332512.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8584900 + 12938409 = 2930^2 + 3597^2 .

It is a cyclic number.

It is not a de Polignac number, because 21523309 - 2⁵ = 21523277 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 (21523339) 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, 633022 + ... + 633055.

It is an arithmetic number, because the mean of its divisors is an integer number (5697351).

Almost surely, 2^21523309 is an apocalyptic number.

It is an amenable number.

21523309 is a deficient number, since it is larger than the sum of its proper divisors (1266095).

21523309 is a wasteful number, since it uses less digits than its factorization.

21523309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1266094.

The product of its (nonzero) digits is 1620, while the sum is 25.

The square root of 21523309 is about 4639.3220409883. The cubic root of 21523309 is about 278.1653390802.

The spelling of 21523309 in words is "twenty-one million, five hundred twenty-three thousand, three hundred nine".