821816 has 16 divisors (see below), whose sum is σ = 1577400. Its totient is φ = 401184.

The previous prime is 821809. The next prime is 821819. The reversal of 821816 is 618128.

821816 = T₉₃ + T₉₄ + ... + T₁₇₈.

It is a plaindrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821819) by changing a digit.

821816 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 in 3 ways as a sum of consecutive naturals, for example, 851 + ... + 1538.

2⁸²¹⁸¹⁶ is an apocalyptic number.

821816 is a gapful number since it is divisible by the number (86) formed by its first and last digit.

It is an amenable number.

821816 is a deficient number, since it is larger than the sum of its proper divisors (755584).

821816 is a wasteful number, since it uses less digits than its factorization.

821816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2438 (or 2434 counting only the distinct ones).

The product of its digits is 768, while the sum is 26.

The square root of 821816 is about 906.5406775209. The cubic root of 821816 is about 93.6680611459.

The spelling of 821816 in words is "eight hundred twenty-one thousand, eight hundred sixteen".