2115821 has 6 divisors (see below), whose sum is σ = 2233422. Its totient is φ = 2004120.

The previous prime is 2115791. The next prime is 2115823. The reversal of 2115821 is 1285112.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 1768900 + 346921 = 1330^2 + 589^2 .

It is not a de Polignac number, because 2115821 - 2¹⁰ = 2114797 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 2115793 and 2115802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2115823) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2570 + ... + 3291.

It is an arithmetic number, because the mean of its divisors is an integer number (372237).

2^2115821 is an apocalyptic number.

It is an amenable number.

2115821 is a deficient number, since it is larger than the sum of its proper divisors (117601).

2115821 is an equidigital number, since it uses as much as digits as its factorization.

2115821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5899 (or 5880 counting only the distinct ones).

The product of its digits is 160, while the sum is 20.

The square root of 2115821 is about 1454.5861954522. The cubic root of 2115821 is about 128.3787002514.

The spelling of 2115821 in words is "two million, one hundred fifteen thousand, eight hundred twenty-one".