79821 has 18 divisors (see below), whose sum is σ = 134862. Its totient is φ = 45360.

The previous prime is 79817. The next prime is 79823. The reversal of 79821 is 12897.

79821 = T₆₃ + T₆₄ + ... + T₈₉.

It can be written as a sum of positive squares in only one way, i.e., 44100 + 35721 = 210^2 + 189^2 .

It is not a de Polignac number, because 79821 - 2² = 79817 is a prime.

It is a plaindrome in base 16.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (79823) 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 17 ways as a sum of consecutive naturals, for example, 351 + ... + 531.

2⁷⁹⁸²¹ is an apocalyptic number.

It is an amenable number.

79821 is a deficient number, since it is larger than the sum of its proper divisors (55041).

79821 is a wasteful number, since it uses less digits than its factorization.

79821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 201 (or 191 counting only the distinct ones).

The product of its digits is 1008, while the sum is 27.

The square root of 79821 is about 282.5261049885. The cubic root of 79821 is about 43.0565328178.

It can be divided in two parts, 79 and 821, that added together give a square (900 = 30²).

The spelling of 79821 in words is "seventy-nine thousand, eight hundred twenty-one".