21408457 has 8 divisors (see below), whose sum is σ = 25906176. Its totient is φ = 17270592.

The previous prime is 21408451. The next prime is 21408461. The reversal of 21408457 is 75480412.

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

It is a cyclic number.

It is not a de Polignac number, because 21408457 - 2⁷ = 21408329 is a prime.

It is a super-2 number, since 2×21408457² = 916644062241698, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21408451) 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, 89833 + ... + 90070.

It is an arithmetic number, because the mean of its divisors is an integer number (3238272).

Almost surely, 2^21408457 is an apocalyptic number.

It is an amenable number.

21408457 is a deficient number, since it is larger than the sum of its proper divisors (4497719).

21408457 is a wasteful number, since it uses less digits than its factorization.

21408457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179927.

The product of its (nonzero) digits is 8960, while the sum is 31.

The square root of 21408457 is about 4626.9273821836. The cubic root of 21408457 is about 277.6696773621.

Adding to 21408457 its reverse (75480412), we get a palindrome (96888869).

The spelling of 21408457 in words is "twenty-one million, four hundred eight thousand, four hundred fifty-seven".