21424531 has 4 divisors (see below), whose sum is σ = 21438064. Its totient is φ = 21411000.

The previous prime is 21424511. The next prime is 21424547. The reversal of 21424531 is 13542412.

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 21424531 - 2⁵ = 21424499 is a prime.

It is a super-2 number, since 2×21424531² = 918021057139922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21424511) 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, 4020 + ... + 7681.

It is an arithmetic number, because the mean of its divisors is an integer number (5359516).

Almost surely, 2^21424531 is an apocalyptic number.

21424531 is a deficient number, since it is larger than the sum of its proper divisors (13533).

21424531 is a wasteful number, since it uses less digits than its factorization.

21424531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13532.

The product of its digits is 960, while the sum is 22.

The square root of 21424531 is about 4628.6640621242. The cubic root of 21424531 is about 277.7391537349.

Adding to 21424531 its reverse (13542412), we get a palindrome (34966943).

The spelling of 21424531 in words is "twenty-one million, four hundred twenty-four thousand, five hundred thirty-one".