123821 has 2 divisors, whose sum is σ = 123822. Its totient is φ = 123820.

The previous prime is 123817. The next prime is 123829. The reversal of 123821 is 128321.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81796 + 42025 = 286^2 + 205^2 .

It is an emirp because it is prime and its reverse (128321) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 123821 - 2² = 123817 is a prime.

It is equal to p₁₁₆₃₆ and since 123821 and 11636 have the same sum of digits, it is a Honaker prime.

It is a plaindrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 123821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (123829) 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 as a sum of consecutive naturals, namely, 61910 + 61911.

It is an arithmetic number, because the mean of its divisors is an integer number (61911).

2¹²³⁸²¹ is an apocalyptic number.

It is an amenable number.

123821 is a deficient number, since it is larger than the sum of its proper divisors (1).

123821 is an equidigital number, since it uses as much as digits as its factorization.

123821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 96, while the sum is 17.

The square root of 123821 is about 351.8820825220. The cubic root of 123821 is about 49.8423031570.

The spelling of 123821 in words is "one hundred twenty-three thousand, eight hundred twenty-one".