21531613 has 4 divisors (see below), whose sum is σ = 21566368. Its totient is φ = 21496860.

The previous prime is 21531599. The next prime is 21531619. The reversal of 21531613 is 31613512.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21531613 - 2⁹ = 21531101 is a prime.

It is a super-2 number, since 2×21531613² = 927220716763538, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531619) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16431 + ... + 17692.

It is an arithmetic number, because the mean of its divisors is an integer number (5391592).

Almost surely, 2^21531613 is an apocalyptic number.

It is an amenable number.

21531613 is a deficient number, since it is larger than the sum of its proper divisors (34755).

21531613 is an equidigital number, since it uses as much as digits as its factorization.

21531613 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34754.

The product of its digits is 540, while the sum is 22.

The square root of 21531613 is about 4640.2169130333. The cubic root of 21531613 is about 278.2011078673.

The spelling of 21531613 in words is "twenty-one million, five hundred thirty-one thousand, six hundred thirteen".