172821 has 8 divisors (see below), whose sum is σ = 251424. Its totient is φ = 104720.

The previous prime is 172807. The next prime is 172829. The reversal of 172821 is 128271.

172821 is nontrivially palindromic in base 2.

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

It is not a de Polignac number, because 172821 - 2¹¹ = 170773 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (172829) 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, 2586 + ... + 2651.

It is an arithmetic number, because the mean of its divisors is an integer number (31428).

2¹⁷²⁸²¹ is an apocalyptic number.

172821 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

172821 is a deficient number, since it is larger than the sum of its proper divisors (78603).

172821 is a wasteful number, since it uses less digits than its factorization.

172821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5251.

The product of its digits is 224, while the sum is 21.

The square root of 172821 is about 415.7174521234. The cubic root of 172821 is about 55.7013222399.

The spelling of 172821 in words is "one hundred seventy-two thousand, eight hundred twenty-one".