2156561 has 4 divisors (see below), whose sum is σ = 2352624. Its totient is φ = 1960500.

The previous prime is 2156537. The next prime is 2156597. The reversal of 2156561 is 1656512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2156561 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 2156561.

It is not an unprimeable number, because it can be changed into a prime (2156521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 98015 + ... + 98036.

It is an arithmetic number, because the mean of its divisors is an integer number (588156).

2^2156561 is an apocalyptic number.

It is an amenable number.

2156561 is a deficient number, since it is larger than the sum of its proper divisors (196063).

2156561 is a wasteful number, since it uses less digits than its factorization.

2156561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 196062.

The product of its digits is 1800, while the sum is 26.

The square root of 2156561 is about 1468.5234080531. The cubic root of 2156561 is about 129.1974421754.

It can be divided in two parts, 215 and 6561, that added together give a palindrome (6776).

The spelling of 2156561 in words is "two million, one hundred fifty-six thousand, five hundred sixty-one".