1981643 has 4 divisors (see below), whose sum is σ = 2085960. Its totient is φ = 1877328.

The previous prime is 1981631. The next prime is 1981649. The reversal of 1981643 is 3461891.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 3461891 = 23 ⋅150517.

It is a cyclic number.

It is not a de Polignac number, because 1981643 - 2⁴ = 1981627 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1981649) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 52130 + ... + 52167.

It is an arithmetic number, because the mean of its divisors is an integer number (521490).

2^1981643 is an apocalyptic number.

1981643 is a deficient number, since it is larger than the sum of its proper divisors (104317).

1981643 is a wasteful number, since it uses less digits than its factorization.

1981643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 104316.

The product of its digits is 5184, while the sum is 32.

The square root of 1981643 is about 1407.7084215135. The cubic root of 1981643 is about 125.6054467393.

The spelling of 1981643 in words is "one million, nine hundred eighty-one thousand, six hundred forty-three".