21057851 has 4 divisors (see below), whose sum is σ = 21067512. Its totient is φ = 21048192.

The previous prime is 21057821. The next prime is 21057877. The reversal of 21057851 is 15875012.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21057851 - 2⁶ = 21057787 is a prime.

It is a super-3 number, since 3×21057851³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21057821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 155 + ... + 6491.

It is an arithmetic number, because the mean of its divisors is an integer number (5266878).

Almost surely, 2^21057851 is an apocalyptic number.

21057851 is a deficient number, since it is larger than the sum of its proper divisors (9661).

21057851 is an equidigital number, since it uses as much as digits as its factorization.

21057851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9660.

The product of its (nonzero) digits is 2800, while the sum is 29.

The square root of 21057851 is about 4588.8834153855. The cubic root of 21057851 is about 276.1455290422.

The spelling of 21057851 in words is "twenty-one million, fifty-seven thousand, eight hundred fifty-one".