1998891217 has 4 divisors (see below), whose sum is σ = 1998983920. Its totient is φ = 1998798516.

The previous prime is 1998891179. The next prime is 1998891221. The reversal of 1998891217 is 7121988991.

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, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 7121988991 = 13 ⋅547845307.

It is a cyclic number.

It is not a de Polignac number, because 1998891217 - 2¹¹ = 1998889169 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1998891287) 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, 4834 + ... + 63412.

It is an arithmetic number, because the mean of its divisors is an integer number (499745980).

Almost surely, 2^1998891217 is an apocalyptic number.

It is an amenable number.

1998891217 is a deficient number, since it is larger than the sum of its proper divisors (92703).

1998891217 is an equidigital number, since it uses as much as digits as its factorization.

1998891217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92702.

The product of its digits is 653184, while the sum is 55.

The square root of 1998891217 is about 44708.9612605795. The cubic root of 1998891217 is about 1259.6881770151.

The spelling of 1998891217 in words is "one billion, nine hundred ninety-eight million, eight hundred ninety-one thousand, two hundred seventeen".