21870205 has 24 divisors (see below), whose sum is σ = 31105152. Its totient is φ = 14460096.

The previous prime is 21870193. The next prime is 21870209. The reversal of 21870205 is 50207812.

It is not a de Polignac number, because 21870205 - 2⁹ = 21869693 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21870205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21870209) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 29064 + ... + 29806.

It is an arithmetic number, because the mean of its divisors is an integer number (1296048).

Almost surely, 2^21870205 is an apocalyptic number.

It is an amenable number.

21870205 is a deficient number, since it is larger than the sum of its proper divisors (9234947).

21870205 is an equidigital number, since it uses as much as digits as its factorization.

21870205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 813 (or 784 counting only the distinct ones).

The product of its (nonzero) digits is 1120, while the sum is 25.

The square root of 21870205 is about 4676.5590983115. The cubic root of 21870205 is about 279.6517993091.

The spelling of 21870205 in words is "twenty-one million, eight hundred seventy thousand, two hundred five".