21168121 has 4 divisors (see below), whose sum is σ = 22796452. Its totient is φ = 19539792.

The previous prime is 21168113. The next prime is 21168137. The reversal of 21168121 is 12186112.

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 12524521 + 8643600 = 3539^2 + 2940^2 .

It is a cyclic number.

It is not a de Polignac number, because 21168121 - 2³ = 21168113 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21168092 and 21168101.

It is not an unprimeable number, because it can be changed into a prime (21168101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 814146 + ... + 814171.

It is an arithmetic number, because the mean of its divisors is an integer number (5699113).

Almost surely, 2^21168121 is an apocalyptic number.

It is an amenable number.

21168121 is a deficient number, since it is larger than the sum of its proper divisors (1628331).

21168121 is a wasteful number, since it uses less digits than its factorization.

21168121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1628330.

The product of its digits is 192, while the sum is 22.

The square root of 21168121 is about 4600.8826327130. The cubic root of 21168121 is about 276.6267046037.

Subtracting from 21168121 its reverse (12186112), we obtain a square (8982009 = 2997²).

The spelling of 21168121 in words is "twenty-one million, one hundred sixty-eight thousand, one hundred twenty-one".