1643665 has 8 divisors (see below), whose sum is σ = 1993320. Its totient is φ = 1300992.

The previous prime is 1643659. The next prime is 1643669. The reversal of 1643665 is 5663461.

It can be written as a sum of positive squares in 4 ways, for example, as 528529 + 1115136 = 727^2 + 1056^2 .

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 1643665 - 2¹¹ = 1641617 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1643669) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1210 + ... + 2179.

It is an arithmetic number, because the mean of its divisors is an integer number (249165).

It is a Poulet number, since it divides 2^1643664-1.

2^1643665 is an apocalyptic number.

It is an amenable number.

1643665 is a deficient number, since it is larger than the sum of its proper divisors (349655).

1643665 is an equidigital number, since it uses as much as digits as its factorization.

1643665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3491.

The product of its digits is 12960, while the sum is 31.

The square root of 1643665 is about 1282.0549910203. The cubic root of 1643665 is about 118.0151517458.

It can be divided in two parts, 16 and 43665, that added together give a square (43681 = 209²).

The spelling of 1643665 in words is "one million, six hundred forty-three thousand, six hundred sixty-five".