21013531 has 8 divisors (see below), whose sum is σ = 26198784. Its totient is φ = 16374120.

The previous prime is 21013529. The next prime is 21013537. The reversal of 21013531 is 13531012.

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

It is not a de Polignac number, because 21013531 - 2¹ = 21013529 is a prime.

It is a super-2 number, since 2×21013531² = 883136970175922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21013537) 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, 136375 + ... + 136528.

It is an arithmetic number, because the mean of its divisors is an integer number (3274848).

Almost surely, 2^21013531 is an apocalyptic number.

21013531 is a deficient number, since it is larger than the sum of its proper divisors (5185253).

21013531 is a wasteful number, since it uses less digits than its factorization.

21013531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 272921.

The product of its (nonzero) digits is 90, while the sum is 16.

The square root of 21013531 is about 4584.0518103529. The cubic root of 21013531 is about 275.9516604763.

Adding to 21013531 its reverse (13531012), we get a palindrome (34544543).

The spelling of 21013531 in words is "twenty-one million, thirteen thousand, five hundred thirty-one".