21408791 has 4 divisors (see below), whose sum is σ = 22339632. Its totient is φ = 20477952.

The previous prime is 21408787. The next prime is 21408823. The reversal of 21408791 is 19780412.

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

It is a cyclic number.

It is not a de Polignac number, because 21408791 - 2² = 21408787 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 (21408721) 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, 465386 + ... + 465431.

It is an arithmetic number, because the mean of its divisors is an integer number (5584908).

Almost surely, 2^21408791 is an apocalyptic number.

21408791 is a deficient number, since it is larger than the sum of its proper divisors (930841).

21408791 is an equidigital number, since it uses as much as digits as its factorization.

21408791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 930840.

The product of its (nonzero) digits is 4032, while the sum is 32.

The square root of 21408791 is about 4626.9634751098. The cubic root of 21408791 is about 277.6711213583.

The spelling of 21408791 in words is "twenty-one million, four hundred eight thousand, seven hundred ninety-one".