821749 has 4 divisors (see below), whose sum is σ = 823564. Its totient is φ = 819936.

The previous prime is 821747. The next prime is 821753. The reversal of 821749 is 947128.

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.

It can be written as a sum of positive squares in 2 ways, for example, as 338724 + 483025 = 582^2 + 695^2 .

It is a cyclic number.

It is not a de Polignac number, because 821749 - 2¹ = 821747 is a prime.

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 821749.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 409 + ... + 1345.

It is an arithmetic number, because the mean of its divisors is an integer number (205891).

2⁸²¹⁷⁴⁹ is an apocalyptic number.

It is an amenable number.

821749 is a deficient number, since it is larger than the sum of its proper divisors (1815).

821749 is an equidigital number, since it uses as much as digits as its factorization.

821749 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1814.

The product of its digits is 4032, while the sum is 31.

The square root of 821749 is about 906.5037231032. The cubic root of 821749 is about 93.6655155920.

The spelling of 821749 in words is "eight hundred twenty-one thousand, seven hundred forty-nine".