21318021 has 12 divisors (see below), whose sum is σ = 30835948. Its totient is φ = 14192064.

The previous prime is 21318007. The next prime is 21318047. The reversal of 21318021 is 12081312.

It can be written as a sum of positive squares in 2 ways, for example, as 14630625 + 6687396 = 3825^2 + 2586^2 .

It is not a de Polignac number, because 21318021 - 2⁹ = 21317509 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21317985 and 21318003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21318091) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8151 + ... + 10443.

Almost surely, 2^21318021 is an apocalyptic number.

It is an amenable number.

21318021 is a deficient number, since it is larger than the sum of its proper divisors (9517927).

21318021 is a wasteful number, since it uses less digits than its factorization.

21318021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3332 (or 3329 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21318021 is about 4617.1442472593. The cubic root of 21318021 is about 277.2781377394.

Adding to 21318021 its reverse (12081312), we get a palindrome (33399333).

The spelling of 21318021 in words is "twenty-one million, three hundred eighteen thousand, twenty-one".