20851819 has 4 divisors (see below), whose sum is σ = 20908096. Its totient is φ = 20795544.

The previous prime is 20851801. The next prime is 20851867. The reversal of 20851819 is 91815802.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20851819 - 2²¹ = 18754667 is a prime.

It is a super-2 number, since 2×20851819² = 869596711217522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20858819) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27579 + ... + 28324.

It is an arithmetic number, because the mean of its divisors is an integer number (5227024).

Almost surely, 2^20851819 is an apocalyptic number.

20851819 is a deficient number, since it is larger than the sum of its proper divisors (56277).

20851819 is an equidigital number, since it uses as much as digits as its factorization.

20851819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 56276.

The product of its (nonzero) digits is 5760, while the sum is 34.

The square root of 20851819 is about 4566.3792001979. The cubic root of 20851819 is about 275.2419644506.

The spelling of 20851819 in words is "twenty million, eight hundred fifty-one thousand, eight hundred nineteen".