1978639 has 4 divisors (see below), whose sum is σ = 2130856. Its totient is φ = 1826424.

The previous prime is 1978631. The next prime is 1978661. The reversal of 1978639 is 9368791.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 9368791 = 83 ⋅112877.

It is a cyclic number.

It is not a de Polignac number, because 1978639 - 2³ = 1978631 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 1978595 and 1978604.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1978631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 76089 + ... + 76114.

It is an arithmetic number, because the mean of its divisors is an integer number (532714).

2^1978639 is an apocalyptic number.

1978639 is a deficient number, since it is larger than the sum of its proper divisors (152217).

1978639 is a wasteful number, since it uses less digits than its factorization.

1978639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 152216.

The product of its digits is 81648, while the sum is 43.

The square root of 1978639 is about 1406.6410345216. The cubic root of 1978639 is about 125.5419456305.

It can be divided in two parts, 197 and 8639, that added together give a square (8836 = 94²).

The spelling of 1978639 in words is "one million, nine hundred seventy-eight thousand, six hundred thirty-nine".