21138021 has 12 divisors (see below), whose sum is σ = 32328972. Its totient is φ = 13262976.

The previous prime is 21138017. The next prime is 21138023. The reversal of 21138021 is 12083112.

It can be written as a sum of positive squares in 2 ways, for example, as 9235521 + 11902500 = 3039^2 + 3450^2 .

It is not a de Polignac number, because 21138021 - 2² = 21138017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21137985 and 21138003.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21138023) 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, 68926 + ... + 69231.

It is an arithmetic number, because the mean of its divisors is an integer number (2694081).

Almost surely, 2^21138021 is an apocalyptic number.

It is an amenable number.

21138021 is a deficient number, since it is larger than the sum of its proper divisors (11190951).

21138021 is a wasteful number, since it uses less digits than its factorization.

21138021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 138180 (or 138177 counting only the distinct ones).

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

The square root of 21138021 is about 4597.6103575662. The cubic root of 21138021 is about 276.4955260022.

The spelling of 21138021 in words is "twenty-one million, one hundred thirty-eight thousand, twenty-one".