2158821 has 12 divisors (see below), whose sum is σ = 3563872. Its totient is φ = 1233576.

The previous prime is 2158817. The next prime is 2158823. The reversal of 2158821 is 1288512.

It is not a de Polignac number, because 2158821 - 2² = 2158817 is a prime.

It is a super-2 number, since 2×2158821² = 9321016220082, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2158823) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 17071 + ... + 17196.

2^2158821 is an apocalyptic number.

2158821 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

2158821 is a deficient number, since it is larger than the sum of its proper divisors (1405051).

2158821 is a wasteful number, since it uses less digits than its factorization.

2158821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34280 (or 34277 counting only the distinct ones).

The product of its digits is 1280, while the sum is 27.

The square root of 2158821 is about 1469.2926869756. The cubic root of 2158821 is about 129.2425578761.

It can be divided in two parts, 21588 and 21, that added together give a square (21609 = 147²).

The spelling of 2158821 in words is "two million, one hundred fifty-eight thousand, eight hundred twenty-one".