21557609 has 4 divisors (see below), whose sum is σ = 22692240. Its totient is φ = 20422980.

The previous prime is 21557603. The next prime is 21557621. The reversal of 21557609 is 90675512.

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 21557609 - 2⁴ = 21557593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21557603) 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, 567287 + ... + 567324.

It is an arithmetic number, because the mean of its divisors is an integer number (5673060).

Almost surely, 2^21557609 is an apocalyptic number.

It is an amenable number.

21557609 is a deficient number, since it is larger than the sum of its proper divisors (1134631).

21557609 is a wasteful number, since it uses less digits than its factorization.

21557609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1134630.

The product of its (nonzero) digits is 18900, while the sum is 35.

The square root of 21557609 is about 4643.0172302071. The cubic root of 21557609 is about 278.3130240439.

The spelling of 21557609 in words is "twenty-one million, five hundred fifty-seven thousand, six hundred nine".