21612205 has 4 divisors (see below), whose sum is σ = 25934652. Its totient is φ = 17289760.

The previous prime is 21612191. The next prime is 21612211. The reversal of 21612205 is 50221612.

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

It can be written as a sum of positive squares in 2 ways, for example, as 8838729 + 12773476 = 2973^2 + 3574^2 .

It is not a de Polignac number, because 21612205 - 2⁷ = 21612077 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2161216 + ... + 2161225.

It is an arithmetic number, because the mean of its divisors is an integer number (6483663).

Almost surely, 2^21612205 is an apocalyptic number.

It is an amenable number.

21612205 is a deficient number, since it is larger than the sum of its proper divisors (4322447).

21612205 is an equidigital number, since it uses as much as digits as its factorization.

21612205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4322446.

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 21612205 is about 4648.8928789552. The cubic root of 21612205 is about 278.5477743918.

Adding to 21612205 its reverse (50221612), we get a palindrome (71833817).

It can be divided in two parts, 216 and 12205, that added together give a palindrome (12421).

The spelling of 21612205 in words is "twenty-one million, six hundred twelve thousand, two hundred five".