2157521 has 4 divisors (see below), whose sum is σ = 2284452. Its totient is φ = 2030592.

The previous prime is 2157517. The next prime is 2157523. The reversal of 2157521 is 1257512.

It is a happy number.

2157521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 1860496 + 297025 = 1364^2 + 545^2 .

It is a cyclic number.

It is not a de Polignac number, because 2157521 - 2² = 2157517 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2157523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 63440 + ... + 63473.

It is an arithmetic number, because the mean of its divisors is an integer number (571113).

2^2157521 is an apocalyptic number.

It is an amenable number.

2157521 is a deficient number, since it is larger than the sum of its proper divisors (126931).

2157521 is a wasteful number, since it uses less digits than its factorization.

2157521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 126930.

The product of its digits is 700, while the sum is 23.

The square root of 2157521 is about 1468.8502306226. The cubic root of 2157521 is about 129.2166102158.

Subtracting from 2157521 its reverse (1257512), we obtain a palindrome (900009).

The spelling of 2157521 in words is "two million, one hundred fifty-seven thousand, five hundred twenty-one".