1816561 has 4 divisors (see below), whose sum is σ = 1819300. Its totient is φ = 1813824.

The previous prime is 1816559. The next prime is 1816567. The reversal of 1816561 is 1656181.

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: 1656181 = 499 ⋅3319.

It can be written as a sum of positive squares in 2 ways, for example, as 1040400 + 776161 = 1020^2 + 881^2 .

It is a cyclic number.

It is not a de Polignac number, because 1816561 - 2¹ = 1816559 is a prime.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1816567) 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, 325 + ... + 1933.

It is an arithmetic number, because the mean of its divisors is an integer number (454825).

2^1816561 is an apocalyptic number.

It is an amenable number.

1816561 is a deficient number, since it is larger than the sum of its proper divisors (2739).

1816561 is a wasteful number, since it uses less digits than its factorization.

1816561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2738.

The product of its digits is 1440, while the sum is 28.

The square root of 1816561 is about 1347.7985754555. The cubic root of 1816561 is about 122.0159658403.

The spelling of 1816561 in words is "one million, eight hundred sixteen thousand, five hundred sixty-one".