21042442021 has 8 divisors (see below), whose sum is σ = 21880837080. Its totient is φ = 20211566592.

The previous prime is 21042441991. The next prime is 21042442027. The reversal of 21042442021 is 12024424012.

It can be written as a sum of positive squares in 4 ways, for example, as 6392002500 + 14650439521 = 79950^2 + 121039^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21042442021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21042441983 and 21042442001.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21042442027) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1874200 + ... + 1885393.

It is an arithmetic number, because the mean of its divisors is an integer number (2735104635).

Almost surely, 2^21042442021 is an apocalyptic number.

It is an amenable number.

21042442021 is a deficient number, since it is larger than the sum of its proper divisors (838395059).

21042442021 is a wasteful number, since it uses less digits than its factorization.

21042442021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3759815.

The product of its (nonzero) digits is 1024, while the sum is 22.

Adding to 21042442021 its reverse (12024424012), we get a palindrome (33066866033).

The spelling of 21042442021 in words is "twenty-one billion, forty-two million, four hundred forty-two thousand, twenty-one".