21860209 has 8 divisors (see below), whose sum is σ = 25143488. Its totient is φ = 18617040.

The previous prime is 21860191. The next prime is 21860219. The reversal of 21860209 is 90206812.

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 21860209 - 2¹⁷ = 21729137 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21860219) 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, 8847 + ... + 11044.

It is an arithmetic number, because the mean of its divisors is an integer number (3142936).

Almost surely, 2^21860209 is an apocalyptic number.

It is an amenable number.

21860209 is a deficient number, since it is larger than the sum of its proper divisors (3283279).

21860209 is a wasteful number, since it uses less digits than its factorization.

21860209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20055.

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

The square root of 21860209 is about 4675.4902416752. The cubic root of 21860209 is about 279.6091869150.

The spelling of 21860209 in words is "twenty-one million, eight hundred sixty thousand, two hundred nine".