21312205 has 16 divisors (see below), whose sum is σ = 27054720. Its totient is φ = 16072128.

The previous prime is 21312173. The next prime is 21312223. The reversal of 21312205 is 50221312.

It is a cyclic number.

It is not a de Polignac number, because 21312205 - 2⁵ = 21312173 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24559 + ... + 25411.

It is an arithmetic number, because the mean of its divisors is an integer number (1690920).

Almost surely, 2^21312205 is an apocalyptic number.

It is an amenable number.

21312205 is a deficient number, since it is larger than the sum of its proper divisors (5742515).

21312205 is a wasteful number, since it uses less digits than its factorization.

21312205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1140.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21312205 is about 4616.5143777530. The cubic root of 21312205 is about 277.2529196962.

Adding to 21312205 its reverse (50221312), we get a palindrome (71533517).

The spelling of 21312205 in words is "twenty-one million, three hundred twelve thousand, two hundred five".