21523409 has 4 divisors (see below), whose sum is σ = 22656240. Its totient is φ = 20390580.

The previous prime is 21523399. The next prime is 21523417. The reversal of 21523409 is 90432512.

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 21523409 - 2¹² = 21519313 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21523499) 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, 566387 + ... + 566424.

It is an arithmetic number, because the mean of its divisors is an integer number (5664060).

Almost surely, 2^21523409 is an apocalyptic number.

It is an amenable number.

21523409 is a deficient number, since it is larger than the sum of its proper divisors (1132831).

21523409 is a wasteful number, since it uses less digits than its factorization.

21523409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1132830.

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 21523409 is about 4639.3328184126. The cubic root of 21523409 is about 278.1657698765.

The spelling of 21523409 in words is "twenty-one million, five hundred twenty-three thousand, four hundred nine".