1981639 has 8 divisors (see below), whose sum is σ = 2289168. Its totient is φ = 1695360.

The previous prime is 1981631. The next prime is 1981649. The reversal of 1981639 is 9361891.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1981639 - 2³ = 1981631 is a prime.

It is a Duffinian number.

It is a zygodrome in base 2.

It is a junction number, because it is equal to n+sod(n) for n = 1981598 and 1981607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1981631) 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 7 ways as a sum of consecutive naturals, for example, 5112 + ... + 5485.

It is an arithmetic number, because the mean of its divisors is an integer number (286146).

2^1981639 is an apocalyptic number.

1981639 is a deficient number, since it is larger than the sum of its proper divisors (307529).

1981639 is a wasteful number, since it uses less digits than its factorization.

1981639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10625.

The product of its digits is 11664, while the sum is 37.

The square root of 1981639 is about 1407.7070007640. The cubic root of 1981639 is about 125.6053622266.

The spelling of 1981639 in words is "one million, nine hundred eighty-one thousand, six hundred thirty-nine".