2106821 has 4 divisors (see below), whose sum is σ = 2179500. Its totient is φ = 2034144.

The previous prime is 2106809. The next prime is 2106829. The reversal of 2106821 is 1286012.

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 829921 + 1276900 = 911^2 + 1130^2 .

It is a cyclic number.

It is not a de Polignac number, because 2106821 - 2¹⁸ = 1844677 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 2106793 and 2106802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2106829) 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, 36296 + ... + 36353.

It is an arithmetic number, because the mean of its divisors is an integer number (544875).

2^2106821 is an apocalyptic number.

It is an amenable number.

2106821 is a deficient number, since it is larger than the sum of its proper divisors (72679).

2106821 is an equidigital number, since it uses as much as digits as its factorization.

2106821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72678.

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

The square root of 2106821 is about 1451.4892352339. The cubic root of 2106821 is about 128.1964147579.

The spelling of 2106821 in words is "two million, one hundred six thousand, eight hundred twenty-one".