21408437 has 4 divisors (see below), whose sum is σ = 21930636. Its totient is φ = 20886240.

The previous prime is 21408433. The next prime is 21408451. The reversal of 21408437 is 73480412.

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 2390116 + 19018321 = 1546^2 + 4361^2 .

It is a cyclic number.

It is not a de Polignac number, because 21408437 - 2² = 21408433 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21408433) 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, 261038 + ... + 261119.

It is an arithmetic number, because the mean of its divisors is an integer number (5482659).

Almost surely, 2^21408437 is an apocalyptic number.

It is an amenable number.

21408437 is a deficient number, since it is larger than the sum of its proper divisors (522199).

21408437 is an equidigital number, since it uses as much as digits as its factorization.

21408437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 522198.

The product of its (nonzero) digits is 5376, while the sum is 29.

The square root of 21408437 is about 4626.9252209216. The cubic root of 21408437 is about 277.6695908948.

Adding to 21408437 its reverse (73480412), we get a palindrome (94888849).

The spelling of 21408437 in words is "twenty-one million, four hundred eight thousand, four hundred thirty-seven".