21424537 has 4 divisors (see below), whose sum is σ = 21493300. Its totient is φ = 21355776.

The previous prime is 21424511. The next prime is 21424547. The reversal of 21424537 is 73542412.

21424537 is nontrivially palindromic in base 13.

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

It can be written as a sum of positive squares in 2 ways, for example, as 594441 + 20830096 = 771^2 + 4564^2 .

It is a cyclic number.

It is not a de Polignac number, because 21424537 - 2⁷ = 21424409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21424547) 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, 33912 + ... + 34537.

It is an arithmetic number, because the mean of its divisors is an integer number (5373325).

Almost surely, 2^21424537 is an apocalyptic number.

It is an amenable number.

21424537 is a deficient number, since it is larger than the sum of its proper divisors (68763).

21424537 is an equidigital number, since it uses as much as digits as its factorization.

21424537 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68762.

The product of its digits is 6720, while the sum is 28.

The square root of 21424537 is about 4628.6647102593. The cubic root of 21424537 is about 277.7391796621.

Adding to 21424537 its reverse (73542412), we get a palindrome (94966949).

The spelling of 21424537 in words is "twenty-one million, four hundred twenty-four thousand, five hundred thirty-seven".