21252121 has 4 divisors (see below), whose sum is σ = 23184144. Its totient is φ = 19320100.

The previous prime is 21252113. The next prime is 21252137. The reversal of 21252121 is 12125212.

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 21252121 - 2³ = 21252113 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21252095 and 21252104.

It is not an unprimeable number, because it can be changed into a prime (21252151) 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, 965995 + ... + 966016.

It is an arithmetic number, because the mean of its divisors is an integer number (5796036).

Almost surely, 2^21252121 is an apocalyptic number.

It is an amenable number.

21252121 is a deficient number, since it is larger than the sum of its proper divisors (1932023).

21252121 is a wasteful number, since it uses less digits than its factorization.

21252121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1932022.

The product of its digits is 80, while the sum is 16.

The square root of 21252121 is about 4610.0022776567. The cubic root of 21252121 is about 276.9921279156.

Adding to 21252121 its reverse (12125212), we get a palindrome (33377333).

The spelling of 21252121 in words is "twenty-one million, two hundred fifty-two thousand, one hundred twenty-one".