21405857 has 8 divisors (see below), whose sum is σ = 24157440. Its totient is φ = 18788560.

The previous prime is 21405829. The next prime is 21405871. The reversal of 21405857 is 75850412.

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 21405857 - 2¹² = 21401761 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21405827) 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, 33233 + ... + 33870.

It is an arithmetic number, because the mean of its divisors is an integer number (3019680).

Almost surely, 2^21405857 is an apocalyptic number.

It is an amenable number.

21405857 is a deficient number, since it is larger than the sum of its proper divisors (2751583).

21405857 is a wasteful number, since it uses less digits than its factorization.

21405857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67143.

The product of its (nonzero) digits is 11200, while the sum is 32.

The square root of 21405857 is about 4626.6464096579. The cubic root of 21405857 is about 277.6584361598.

It can be divided in two parts, 2140 and 5857, that added together give a palindrome (7997).

The spelling of 21405857 in words is "twenty-one million, four hundred five thousand, eight hundred fifty-seven".