1998990 has 96 divisors (see below), whose sum is σ = 6289920. Its totient is φ = 430272.

The previous prime is 1998977. The next prime is 1998991. The reversal of 1998990 is 998991.

It is a super-2 number, since 2×1998990² = 7991922040200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1998991) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 11887 + ... + 12053.

It is an arithmetic number, because the mean of its divisors is an integer number (65520).

2^1998990 is an apocalyptic number.

1998990 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 1998990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3144960).

1998990 is an abundant number, since it is smaller than the sum of its proper divisors (4290930).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1998990 is a wasteful number, since it uses less digits than its factorization.

1998990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 206 (or 203 counting only the distinct ones).

The product of its (nonzero) digits is 52488, while the sum is 45.

The square root of 1998990 is about 1413.8564283547. The cubic root of 1998990 is about 125.9708927474.

Subtracting from 1998990 its reverse (998991), we obtain a palindrome (999999).

It can be divided in two parts, 1 and 998990, that added together give a triangular number (998991 = T₁₄₁₃).

The spelling of 1998990 in words is "one million, nine hundred ninety-eight thousand, nine hundred ninety".