1643561 has 4 divisors (see below), whose sum is σ = 1647300. Its totient is φ = 1639824.

The previous prime is 1643539. The next prime is 1643581. The reversal of 1643561 is 1653461.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1653461 = 907 ⋅1823.

It can be written as a sum of positive squares in 2 ways, for example, as 931225 + 712336 = 965^2 + 844^2 .

It is a cyclic number.

It is not a de Polignac number, because 1643561 - 2⁶ = 1643497 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1643561.

It is not an unprimeable number, because it can be changed into a prime (1643501) 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, 1106 + ... + 2123.

It is an arithmetic number, because the mean of its divisors is an integer number (411825).

2^1643561 is an apocalyptic number.

It is an amenable number.

1643561 is a deficient number, since it is larger than the sum of its proper divisors (3739).

1643561 is an equidigital number, since it uses as much as digits as its factorization.

1643561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3738.

The product of its digits is 2160, while the sum is 26.

The square root of 1643561 is about 1282.0144304960. The cubic root of 1643561 is about 118.0126626266.

The spelling of 1643561 in words is "one million, six hundred forty-three thousand, five hundred sixty-one".