2157581 has 4 divisors (see below), whose sum is σ = 2215932. Its totient is φ = 2099232.

The previous prime is 2157563. The next prime is 2157587. The reversal of 2157581 is 1857512.

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 1755625 + 401956 = 1325^2 + 634^2 .

It is not a de Polignac number, because 2157581 - 2⁶ = 2157517 is a prime.

It is a super-2 number, since 2×2157581² = 9310311543122, 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 (2157587) 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, 29120 + ... + 29193.

It is an arithmetic number, because the mean of its divisors is an integer number (553983).

2^2157581 is an apocalyptic number.

It is an amenable number.

2157581 is a deficient number, since it is larger than the sum of its proper divisors (58351).

2157581 is an equidigital number, since it uses as much as digits as its factorization.

2157581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58350.

The product of its digits is 2800, while the sum is 29.

The square root of 2157581 is about 1468.8706546187. The cubic root of 2157581 is about 129.2178080295.

It can be divided in two parts, 215 and 7581, that multiplied together give a triangular number (1629915 = T₁₈₀₅).

The spelling of 2157581 in words is "two million, one hundred fifty-seven thousand, five hundred eighty-one".