21408961 has 4 divisors (see below), whose sum is σ = 24467392. Its totient is φ = 18350532.

The previous prime is 21408949. The next prime is 21408971. The reversal of 21408961 is 16980412.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21408961 - 2⁷ = 21408833 is a prime.

It is a super-2 number, since 2×21408961² = 916687222199042, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21408901) 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 3 ways as a sum of consecutive naturals, for example, 1529205 + ... + 1529218.

It is an arithmetic number, because the mean of its divisors is an integer number (6116848).

Almost surely, 2^21408961 is an apocalyptic number.

It is an amenable number.

21408961 is a deficient number, since it is larger than the sum of its proper divisors (3058431).

21408961 is an equidigital number, since it uses as much as digits as its factorization.

21408961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3058430.

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 21408961 is about 4626.9818456527. The cubic root of 21408961 is about 277.6718563206.

The spelling of 21408961 in words is "twenty-one million, four hundred eight thousand, nine hundred sixty-one".