21145121 has 4 divisors (see below), whose sum is σ = 21636912. Its totient is φ = 20653332.

The previous prime is 21145109. The next prime is 21145141. The reversal of 21145121 is 12154112.

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 21145121 - 2¹⁸ = 20882977 is a prime.

It is a super-2 number, since 2×21145121² = 894232284209282, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21145121.

It is not an unprimeable number, because it can be changed into a prime (21145141) 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, 245831 + ... + 245916.

It is an arithmetic number, because the mean of its divisors is an integer number (5409228).

Almost surely, 2^21145121 is an apocalyptic number.

It is an amenable number.

21145121 is a deficient number, since it is larger than the sum of its proper divisors (491791).

21145121 is an equidigital number, since it uses as much as digits as its factorization.

21145121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 491790.

The product of its digits is 80, while the sum is 17.

The square root of 21145121 is about 4598.3824329866. The cubic root of 21145121 is about 276.5264796801.

Adding to 21145121 its reverse (12154112), we get a palindrome (33299233).

The spelling of 21145121 in words is "twenty-one million, one hundred forty-five thousand, one hundred twenty-one".