100021 has 4 divisors (see below), whose sum is σ = 103500. Its totient is φ = 96544.

The previous prime is 100019. The next prime is 100043. The reversal of 100021 is 120001.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 18225 + 81796 = 135^2 + 286^2 .

It is a cyclic number.

It is not a de Polignac number, because 100021 - 2¹ = 100019 is a prime.

It is a Duffinian number.

It is a plaindrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (100621) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1696 + ... + 1753.

It is an arithmetic number, because the mean of its divisors is an integer number (25875).

2¹⁰⁰⁰²¹ is an apocalyptic number.

It is an amenable number.

100021 is a deficient number, since it is larger than the sum of its proper divisors (3479).

100021 is an equidigital number, since it uses as much as digits as its factorization.

100021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3478.

The product of its (nonzero) digits is 2, while the sum is 4.

The square root of 100021 is about 316.2609681892. The cubic root of 100021 is about 46.4191372209.

Adding to 100021 its reverse (120001), we get a palindrome (220022).

Multiplying 100021 by its reverse (120001), we get a palindrome (12002620021).

The spelling of 100021 in words is "one hundred thousand, twenty-one", and thus it is an iban number.