1981689 has 4 divisors (see below), whose sum is σ = 2642256. Its totient is φ = 1321124.

The previous prime is 1981687. The next prime is 1981691. The reversal of 1981689 is 9861891.

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.

It is an interprime number because it is at equal distance from previous prime (1981687) and next prime (1981691).

It is a cyclic number.

It is not a de Polignac number, because 1981689 - 2¹ = 1981687 is a prime.

It is a D-number.

It is a self number, because there is not a number n which added to its sum of digits gives 1981689.

It is not an unprimeable number, because it can be changed into a prime (1981687) 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, 330279 + ... + 330284.

It is an arithmetic number, because the mean of its divisors is an integer number (660564).

2^1981689 is an apocalyptic number.

It is an amenable number.

1981689 is a deficient number, since it is larger than the sum of its proper divisors (660567).

1981689 is an equidigital number, since it uses as much as digits as its factorization.

1981689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 660566.

The product of its digits is 31104, while the sum is 42.

The square root of 1981689 is about 1407.7247600295. The cubic root of 1981689 is about 125.6064186274.

The spelling of 1981689 in words is "one million, nine hundred eighty-one thousand, six hundred eighty-nine".