20857993 has 4 divisors (see below), whose sum is σ = 22462468. Its totient is φ = 19253520.

The previous prime is 20857981. The next prime is 20857999. The reversal of 20857993 is 39975802.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 5702544 + 15155449 = 2388^2 + 3893^2 .

It is not a de Polignac number, because 20857993 - 2⁵ = 20857961 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20857999) 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, 802218 + ... + 802243.

It is an arithmetic number, because the mean of its divisors is an integer number (5615617).

Almost surely, 2^20857993 is an apocalyptic number.

It is an amenable number.

20857993 is a deficient number, since it is larger than the sum of its proper divisors (1604475).

20857993 is a wasteful number, since it uses less digits than its factorization.

20857993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1604474.

The product of its (nonzero) digits is 136080, while the sum is 43.

The square root of 20857993 is about 4567.0551781208. The cubic root of 20857993 is about 275.2691271679.

It can be divided in two parts, 2085799 and 3, that added together give a palindrome (2085802).

The spelling of 20857993 in words is "twenty million, eight hundred fifty-seven thousand, nine hundred ninety-three".