21531021 has 16 divisors (see below), whose sum is σ = 29842560. Its totient is φ = 13791680.

The previous prime is 21531011. The next prime is 21531023. The reversal of 21531021 is 12013512.

It is a cyclic number.

It is not a de Polignac number, because 21531021 - 2⁵ = 21530989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531023) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 22411 + ... + 23351.

It is an arithmetic number, because the mean of its divisors is an integer number (1865160).

Almost surely, 2^21531021 is an apocalyptic number.

It is an amenable number.

21531021 is a deficient number, since it is larger than the sum of its proper divisors (8311539).

21531021 is a wasteful number, since it uses less digits than its factorization.

21531021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1236.

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21531021 is about 4640.1531224734. The cubic root of 21531021 is about 278.1985581812.

Adding to 21531021 its reverse (12013512), we get a palindrome (33544533).

The spelling of 21531021 in words is "twenty-one million, five hundred thirty-one thousand, twenty-one".