21423531 has 4 divisors (see below), whose sum is σ = 28564712. Its totient is φ = 14282352.

The previous prime is 21423527. The next prime is 21423533. The reversal of 21423531 is 13532412.

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

It is not a de Polignac number, because 21423531 - 2² = 21423527 is a prime.

It is a super-2 number, since 2×21423531² = 917935361015922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21423498 and 21423507.

It is not an unprimeable number, because it can be changed into a prime (21423533) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3570586 + ... + 3570591.

It is an arithmetic number, because the mean of its divisors is an integer number (7141178).

Almost surely, 2^21423531 is an apocalyptic number.

21423531 is a deficient number, since it is larger than the sum of its proper divisors (7141181).

21423531 is an equidigital number, since it uses as much as digits as its factorization.

21423531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7141180.

The product of its digits is 720, while the sum is 21.

The square root of 21423531 is about 4628.5560383342. The cubic root of 21423531 is about 277.7348324660.

Adding to 21423531 its reverse (13532412), we get a palindrome (34955943).

The spelling of 21423531 in words is "twenty-one million, four hundred twenty-three thousand, five hundred thirty-one".