1981890 has 72 divisors (see below), whose sum is σ = 5527548. Its totient is φ = 492480.

The previous prime is 1981883. The next prime is 1981891. The reversal of 1981890 is 981891.

It can be written as a sum of positive squares in 2 ways, for example, as 1718721 + 263169 = 1311^2 + 513^2 .

It is not an unprimeable number, because it can be changed into a prime (1981891) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 32460 + ... + 32520.

2^1981890 is an apocalyptic number.

1981890 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 1981890, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2763774).

1981890 is an abundant number, since it is smaller than the sum of its proper divisors (3545658).

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

1981890 is a wasteful number, since it uses less digits than its factorization.

1981890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 112 (or 90 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 36.

The square root of 1981890 is about 1407.7961500160. The cubic root of 1981890 is about 125.6106651795.

Subtracting from 1981890 its reverse (981891), we obtain a palindrome (999999).

The spelling of 1981890 in words is "one million, nine hundred eighty-one thousand, eight hundred ninety".