2161521 has 6 divisors (see below), whose sum is σ = 3122210. Its totient is φ = 1441008.

The previous prime is 2161513. The next prime is 2161553. The reversal of 2161521 is 1251612.

It can be written as a sum of positive squares in only one way, i.e., 2143296 + 18225 = 1464^2 + 135^2 .

It is not a de Polignac number, because 2161521 - 2³ = 2161513 is a prime.

It is a Duffinian number.

2161521 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 2161494 and 2161503.

It is not an unprimeable number, because it can be changed into a prime (2161571) 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, 120076 + ... + 120093.

2^2161521 is an apocalyptic number.

It is an amenable number.

2161521 is a deficient number, since it is larger than the sum of its proper divisors (960689).

2161521 is a wasteful number, since it uses less digits than its factorization.

2161521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 240175 (or 240172 counting only the distinct ones).

The product of its digits is 120, while the sum is 18.

The square root of 2161521 is about 1470.2112093165. The cubic root of 2161521 is about 129.2964159047.

Subtracting from 2161521 its reverse (1251612), we obtain a palindrome (909909).

It can be divided in two parts, 216152 and 1, that added together give a triangular number (216153 = T₆₅₇).

The spelling of 2161521 in words is "two million, one hundred sixty-one thousand, five hundred twenty-one".