561821 has 8 divisors (see below), whose sum is σ = 631680. Its totient is φ = 495792.

The previous prime is 561809. The next prime is 561829. The reversal of 561821 is 128165.

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 561821 - 2¹⁰ = 560797 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 561821.

It is not an unprimeable number, because it can be changed into a prime (561829) 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, 641 + ... + 1238.

It is an arithmetic number, because the mean of its divisors is an integer number (78960).

2⁵⁶¹⁸²¹ is an apocalyptic number.

It is an amenable number.

561821 is a deficient number, since it is larger than the sum of its proper divisors (69859).

561821 is a wasteful number, since it uses less digits than its factorization.

561821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1915.

The product of its digits is 480, while the sum is 23.

The square root of 561821 is about 749.5471966461. The cubic root of 561821 is about 82.5149529064.

Adding to 561821 its reverse (128165), we get a palindrome (689986).

The spelling of 561821 in words is "five hundred sixty-one thousand, eight hundred twenty-one".