21288121 has 4 divisors (see below), whose sum is σ = 21455872. Its totient is φ = 21120372.

The previous prime is 21288119. The next prime is 21288161. The reversal of 21288121 is 12188212.

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 21288121 - 2¹ = 21288119 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21288161) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 83685 + ... + 83938.

It is an arithmetic number, because the mean of its divisors is an integer number (5363968).

Almost surely, 2^21288121 is an apocalyptic number.

It is an amenable number.

21288121 is a deficient number, since it is larger than the sum of its proper divisors (167751).

21288121 is a wasteful number, since it uses less digits than its factorization.

21288121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 167750.

The product of its digits is 512, while the sum is 25.

The square root of 21288121 is about 4613.9051789130. The cubic root of 21288121 is about 277.1484431585.

Subtracting from 21288121 its reverse (12188212), we obtain a palindrome (9099909).

The spelling of 21288121 in words is "twenty-one million, two hundred eighty-eight thousand, one hundred twenty-one".