21408851 has 2 divisors, whose sum is σ = 21408852. Its totient is φ = 21408850.

The previous prime is 21408841. The next prime is 21408901. The reversal of 21408851 is 15880412.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21408851 - 2⁶ = 21408787 is a prime.

It is a super-2 number, since 2×21408851² = 916677802280402, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21408841) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10704425 + 10704426.

It is an arithmetic number, because the mean of its divisors is an integer number (10704426).

Almost surely, 2^21408851 is an apocalyptic number.

21408851 is a deficient number, since it is larger than the sum of its proper divisors (1).

21408851 is an equidigital number, since it uses as much as digits as its factorization.

21408851 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2560, while the sum is 29.

The square root of 21408851 is about 4626.9699588392. The cubic root of 21408851 is about 277.6713807572.

The spelling of 21408851 in words is "twenty-one million, four hundred eight thousand, eight hundred fifty-one".