2156561217 has 12 divisors (see below), whose sum is σ = 3115472724. Its totient is φ = 1437504480.

The previous prime is 2156561203. The next prime is 2156561257. The reversal of 2156561217 is 7121656512.

2156561217 is a `hidden beast` number, since 21 + 5 + 6 + 5 + 612 + 17 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 1797420816 + 359140401 = 42396^2 + 18951^2 .

It is not a de Polignac number, because 2156561217 - 2⁷ = 2156561089 is a prime.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (2156561257) 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, 78967 + ... + 102707.

It is an arithmetic number, because the mean of its divisors is an integer number (259622727).

Almost surely, 2^2156561217 is an apocalyptic number.

It is an amenable number.

2156561217 is a deficient number, since it is larger than the sum of its proper divisors (958911507).

2156561217 is a wasteful number, since it uses less digits than its factorization.

2156561217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33840 (or 33837 counting only the distinct ones).

The product of its digits is 25200, while the sum is 36.

The square root of 2156561217 is about 46438.7900036166. The cubic root of 2156561217 is about 1291.9744650882.

The spelling of 2156561217 in words is "two billion, one hundred fifty-six million, five hundred sixty-one thousand, two hundred seventeen".