21408657 has 8 divisors (see below), whose sum is σ = 28608384. Its totient is φ = 14240688.

The previous prime is 21408623. The next prime is 21408659. The reversal of 21408657 is 75680412.

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

It is not a de Polignac number, because 21408657 - 2⁷ = 21408529 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21408659) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6318 + ... + 9095.

It is an arithmetic number, because the mean of its divisors is an integer number (3576048).

Almost surely, 2^21408657 is an apocalyptic number.

It is an amenable number.

21408657 is a deficient number, since it is larger than the sum of its proper divisors (7199727).

21408657 is a wasteful number, since it uses less digits than its factorization.

21408657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15879.

The product of its (nonzero) digits is 13440, while the sum is 33.

The square root of 21408657 is about 4626.9489947481. The cubic root of 21408657 is about 277.6705420323.

The spelling of 21408657 in words is "twenty-one million, four hundred eight thousand, six hundred fifty-seven".