21406321 has 8 divisors (see below), whose sum is σ = 22521600. Its totient is φ = 20316240.

The previous prime is 21406279. The next prime is 21406339. The reversal of 21406321 is 12360412.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21406321 - 2⁷ = 21406193 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21406361) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4545 + ... + 7966.

It is an arithmetic number, because the mean of its divisors is an integer number (2815200).

Almost surely, 2^21406321 is an apocalyptic number.

It is an amenable number.

21406321 is a deficient number, since it is larger than the sum of its proper divisors (1115279).

21406321 is a wasteful number, since it uses less digits than its factorization.

21406321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12599.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21406321 is about 4626.6965536979. The cubic root of 21406321 is about 277.6604423488.

Adding to 21406321 its reverse (12360412), we get a palindrome (33766733).

The spelling of 21406321 in words is "twenty-one million, four hundred six thousand, three hundred twenty-one".