21206121 has 4 divisors (see below), whose sum is σ = 28274832. Its totient is φ = 14137412.

The previous prime is 21206117. The next prime is 21206131. The reversal of 21206121 is 12160212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21206121 - 2² = 21206117 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21206121.

It is not an unprimeable number, because it can be changed into a prime (21206131) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3534351 + ... + 3534356.

It is an arithmetic number, because the mean of its divisors is an integer number (7068708).

Almost surely, 2^21206121 is an apocalyptic number.

It is an amenable number.

21206121 is a deficient number, since it is larger than the sum of its proper divisors (7068711).

21206121 is an equidigital number, since it uses as much as digits as its factorization.

21206121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7068710.

The product of its (nonzero) digits is 48, while the sum is 15.

The square root of 21206121 is about 4605.0104234410. The cubic root of 21206121 is about 276.7921346694.

Adding to 21206121 its reverse (12160212), we get a palindrome (33366333).

The spelling of 21206121 in words is "twenty-one million, two hundred six thousand, one hundred twenty-one".