1998940717921 has 45 divisors (see below), whose sum is σ = 2492998202319. Its totient is φ = 1597796419968.

The previous prime is 1998940717913. The next prime is 1998940717973. The reversal of 1998940717921 is 1297170498991.

The square root of 1998940717921 is 1413839.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 7 ways, for example, as 14403600225 + 1984537117696 = 120015^2 + 1408736^2 .

It is not a de Polignac number, because 1998940717921 - 2³ = 1998940717913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1998940717321) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 18338905615 + ... + 18338905723.

Almost surely, 2^{1998940717921} is an apocalyptic number.

1998940717921 is the 1413839-th square number.

1998940717921 is the 706920-th centered octagonal number.

It is an amenable number.

1998940717921 is a deficient number, since it is larger than the sum of its proper divisors (494057484398).

1998940717921 is an frugal number, since it uses more digits than its factorization.

1998940717921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 484 (or 133 counting only the distinct ones).

The product of its (nonzero) digits is 20575296, while the sum is 67.

The spelling of 1998940717921 in words is "one trillion, nine hundred ninety-eight billion, nine hundred forty million, seven hundred seventeen thousand, nine hundred twenty-one".