21802121 has 4 divisors (see below), whose sum is σ = 23784144. Its totient is φ = 19820100.

The previous prime is 21802117. The next prime is 21802129. The reversal of 21802121 is 12120812.

It is a happy number.

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 21802121 - 2² = 21802117 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 21802121.

It is not an unprimeable number, because it can be changed into a prime (21802129) 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, 990995 + ... + 991016.

It is an arithmetic number, because the mean of its divisors is an integer number (5946036).

Almost surely, 2^21802121 is an apocalyptic number.

It is an amenable number.

21802121 is a deficient number, since it is larger than the sum of its proper divisors (1982023).

21802121 is a wasteful number, since it uses less digits than its factorization.

21802121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1982022.

The product of its (nonzero) digits is 64, while the sum is 17.

The square root of 21802121 is about 4669.2741405919. The cubic root of 21802121 is about 279.3613035574.

Adding to 21802121 its reverse (12120812), we get a palindrome (33922933).

The spelling of 21802121 in words is "twenty-one million, eight hundred two thousand, one hundred twenty-one".