21798209 has 8 divisors (see below), whose sum is σ = 22070400. Its totient is φ = 21528000.

The previous prime is 21798197. The next prime is 21798221. The reversal of 21798209 is 90289712.

It is an interprime number because it is at equal distance from previous prime (21798197) and next prime (21798221).

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 21798209 - 2⁸ = 21797953 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21798299) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 36092 + ... + 36690.

It is an arithmetic number, because the mean of its divisors is an integer number (2758800).

Almost surely, 2^21798209 is an apocalyptic number.

It is an amenable number.

21798209 is a deficient number, since it is larger than the sum of its proper divisors (272191).

21798209 is a wasteful number, since it uses less digits than its factorization.

21798209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 991.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 21798209 is about 4668.8552130046. The cubic root of 21798209 is about 279.3445937643.

The spelling of 21798209 in words is "twenty-one million, seven hundred ninety-eight thousand, two hundred nine".