216821 has 8 divisors (see below), whose sum is σ = 247104. Its totient is φ = 188320.

The previous prime is 216803. The next prime is 216829. The reversal of 216821 is 128612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 216821 - 2⁶ = 216757 is a prime.

It is a super-2 number, since 2×216821² = 94022692082, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 216793 and 216802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216829) 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, 176 + ... + 681.

It is an arithmetic number, because the mean of its divisors is an integer number (30888).

2²¹⁶⁸²¹ is an apocalyptic number.

It is an amenable number.

216821 is a deficient number, since it is larger than the sum of its proper divisors (30283).

216821 is a wasteful number, since it uses less digits than its factorization.

216821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 891.

The product of its digits is 192, while the sum is 20.

The square root of 216821 is about 465.6404192078. The cubic root of 216821 is about 60.0759224078.

Subtracting from 216821 its reverse (128612), we obtain a square (88209 = 297²).

The spelling of 216821 in words is "two hundred sixteen thousand, eight hundred twenty-one".