21020609 has 4 divisors (see below), whose sum is σ = 21467904. Its totient is φ = 20573316.

The previous prime is 21020603. The next prime is 21020611. The reversal of 21020609 is 90602012.

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 21020609 - 2⁸ = 21020353 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21020603) 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, 223577 + ... + 223670.

It is an arithmetic number, because the mean of its divisors is an integer number (5366976).

Almost surely, 2^21020609 is an apocalyptic number.

It is an amenable number.

21020609 is a deficient number, since it is larger than the sum of its proper divisors (447295).

21020609 is an equidigital number, since it uses as much as digits as its factorization.

21020609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 447294.

The product of its (nonzero) digits is 216, while the sum is 20.

The square root of 21020609 is about 4584.8237697866. The cubic root of 21020609 is about 275.9826399849.

The spelling of 21020609 in words is "twenty-one million, twenty thousand, six hundred nine".