20851921 has 4 divisors (see below), whose sum is σ = 20872192. Its totient is φ = 20831652.

The previous prime is 20851907. The next prime is 20851927. The reversal of 20851921 is 12915802.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20851921 - 2¹⁹ = 20327633 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20851921.

It is not an unprimeable number, because it can be changed into a prime (20851927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8505 + ... + 10678.

It is an arithmetic number, because the mean of its divisors is an integer number (5218048).

Almost surely, 2^20851921 is an apocalyptic number.

It is an amenable number.

20851921 is a deficient number, since it is larger than the sum of its proper divisors (20271).

20851921 is a wasteful number, since it uses less digits than its factorization.

20851921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20270.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 20851921 is about 4566.3903687705. The cubic root of 20851921 is about 275.2424132465.

The spelling of 20851921 in words is "twenty million, eight hundred fifty-one thousand, nine hundred twenty-one".