21121021 has 4 divisors (see below), whose sum is σ = 22363452. Its totient is φ = 19878592.

The previous prime is 21121003. The next prime is 21121033. The reversal of 21121021 is 12012112.

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 10791225 + 10329796 = 3285^2 + 3214^2 .

It is a cyclic number.

It is not a de Polignac number, because 21121021 - 2⁷ = 21120893 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21120989 and 21121007.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121081) 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, 621190 + ... + 621223.

It is an arithmetic number, because the mean of its divisors is an integer number (5590863).

Almost surely, 2^21121021 is an apocalyptic number.

It is an amenable number.

21121021 is a deficient number, since it is larger than the sum of its proper divisors (1242431).

21121021 is a wasteful number, since it uses less digits than its factorization.

21121021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1242430.

The product of its (nonzero) digits is 8, while the sum is 10.

The square root of 21121021 is about 4595.7611991921. The cubic root of 21121021 is about 276.4213833851.

Adding to 21121021 its reverse (12012112), we get a palindrome (33133133).

The spelling of 21121021 in words is "twenty-one million, one hundred twenty-one thousand, twenty-one".