21028609 has 8 divisors (see below), whose sum is σ = 25446528. Its totient is φ = 16964160.

The previous prime is 21028597. The next prime is 21028619. The reversal of 21028609 is 90682012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21028609 - 2⁷ = 21028481 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21028619) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 88237 + ... + 88474.

It is an arithmetic number, because the mean of its divisors is an integer number (3180816).

Almost surely, 2^21028609 is an apocalyptic number.

It is an amenable number.

21028609 is a deficient number, since it is larger than the sum of its proper divisors (4417919).

21028609 is a wasteful number, since it uses less digits than its factorization.

21028609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 176735.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 21028609 is about 4585.6961303601. The cubic root of 21028609 is about 276.0176465998.

The spelling of 21028609 in words is "twenty-one million, twenty-eight thousand, six hundred nine".