821728 has 12 divisors (see below), whose sum is σ = 1617840. Its totient is φ = 410848.

The previous prime is 821677. The next prime is 821741. The reversal of 821728 is 827128.

It is a junction number, because it is equal to n+sod(n) for n = 821696 and 821705.

It is a congruent number.

It is an unprimeable number.

821728 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 12808 + ... + 12871.

It is an arithmetic number, because the mean of its divisors is an integer number (134820).

2⁸²¹⁷²⁸ is an apocalyptic number.

It is an amenable number.

821728 is a deficient number, since it is larger than the sum of its proper divisors (796112).

821728 is a wasteful number, since it uses less digits than its factorization.

821728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25689 (or 25681 counting only the distinct ones).

The product of its digits is 1792, while the sum is 28.

The square root of 821728 is about 906.4921400652. The cubic root of 821728 is about 93.6647177034.

It can be divided in two parts, 8 and 21728, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 821728 in words is "eight hundred twenty-one thousand, seven hundred twenty-eight".