1643921 has 4 divisors (see below), whose sum is σ = 1648932. Its totient is φ = 1638912.

The previous prime is 1643893. The next prime is 1643959. The reversal of 1643921 is 1293461.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1293461 = 13 ⋅99497.

It can be written as a sum of positive squares in 2 ways, for example, as 409600 + 1234321 = 640^2 + 1111^2 .

It is a cyclic number.

It is not a de Polignac number, because 1643921 - 2⁶ = 1643857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1643021) 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, 1976 + ... + 2681.

It is an arithmetic number, because the mean of its divisors is an integer number (412233).

2^1643921 is an apocalyptic number.

It is an amenable number.

1643921 is a deficient number, since it is larger than the sum of its proper divisors (5011).

1643921 is an equidigital number, since it uses as much as digits as its factorization.

1643921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5010.

The product of its digits is 1296, while the sum is 26.

The square root of 1643921 is about 1282.1548268442. The cubic root of 1643921 is about 118.0212783613.

The spelling of 1643921 in words is "one million, six hundred forty-three thousand, nine hundred twenty-one".