21205355 has 4 divisors (see below), whose sum is σ = 25446432. Its totient is φ = 16964280.

The previous prime is 21205313. The next prime is 21205361. The reversal of 21205355 is 55350212.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21205355 - 2⁶ = 21205291 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 21205355.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2120531 + ... + 2120540.

It is an arithmetic number, because the mean of its divisors is an integer number (6361608).

Almost surely, 2^21205355 is an apocalyptic number.

21205355 is a deficient number, since it is larger than the sum of its proper divisors (4241077).

21205355 is an equidigital number, since it uses as much as digits as its factorization.

21205355 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4241076.

The product of its (nonzero) digits is 1500, while the sum is 23.

The square root of 21205355 is about 4604.9272524113. The cubic root of 21205355 is about 276.7888019000.

Adding to 21205355 its reverse (55350212), we get a palindrome (76555567).

The spelling of 21205355 in words is "twenty-one million, two hundred five thousand, three hundred fifty-five".