21109531 has 4 divisors (see below), whose sum is σ = 21142512. Its totient is φ = 21076552.

The previous prime is 21109493. The next prime is 21109549. The reversal of 21109531 is 13590112.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21109531 - 2¹¹ = 21107483 is a prime.

It is a super-2 number, since 2×21109531² = 891224598079922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21109591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15511 + ... + 16816.

It is an arithmetic number, because the mean of its divisors is an integer number (5285628).

Almost surely, 2^21109531 is an apocalyptic number.

21109531 is a deficient number, since it is larger than the sum of its proper divisors (32981).

21109531 is an equidigital number, since it uses as much as digits as its factorization.

21109531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32980.

The product of its (nonzero) digits is 270, while the sum is 22.

The square root of 21109531 is about 4594.5109641832. The cubic root of 21109531 is about 276.3712491640.

Adding to 21109531 its reverse (13590112), we get a palindrome (34699643).

The spelling of 21109531 in words is "twenty-one million, one hundred nine thousand, five hundred thirty-one".