1998821857 has 4 divisors (see below), whose sum is σ = 2016510660. Its totient is φ = 1981133056.

The previous prime is 1998821849. The next prime is 1998821861. The reversal of 1998821857 is 7581288991.

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 890664336 + 1108157521 = 29844^2 + 33289^2 .

It is a cyclic number.

It is not a de Polignac number, because 1998821857 - 2³ = 1998821849 is a prime.

It is a Smith number, since the sum of its digits (58) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1998821837) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8844232 + ... + 8844457.

It is an arithmetic number, because the mean of its divisors is an integer number (504127665).

Almost surely, 2^1998821857 is an apocalyptic number.

It is an amenable number.

1998821857 is a deficient number, since it is larger than the sum of its proper divisors (17688803).

1998821857 is a wasteful number, since it uses less digits than its factorization.

1998821857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17688802.

The product of its digits is 2903040, while the sum is 58.

The square root of 1998821857 is about 44708.1855704299. The cubic root of 1998821857 is about 1259.6736067737.

The spelling of 1998821857 in words is "one billion, nine hundred ninety-eight million, eight hundred twenty-one thousand, eight hundred fifty-seven".