1664639 has 4 divisors (see below), whose sum is σ = 1667256. Its totient is φ = 1662024.

The previous prime is 1664633. The next prime is 1664651. The reversal of 1664639 is 9364661.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 9364661 = 1303 ⋅7187.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1664639 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1664599 and 1664608.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1664633) 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, 332 + ... + 1854.

It is an arithmetic number, because the mean of its divisors is an integer number (416814).

2^1664639 is an apocalyptic number.

1664639 is a deficient number, since it is larger than the sum of its proper divisors (2617).

1664639 is a wasteful number, since it uses less digits than its factorization.

1664639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2616.

The product of its digits is 23328, while the sum is 35.

The square root of 1664639 is about 1290.2088978146. The cubic root of 1664639 is about 118.5150093446.

The spelling of 1664639 in words is "one million, six hundred sixty-four thousand, six hundred thirty-nine".