2218181921 has 4 divisors (see below), whose sum is σ = 2218707732. Its totient is φ = 2217656112.

The previous prime is 2218181909. The next prime is 2218181951. The reversal of 2218181921 is 1291818122.

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 709636321 + 1508545600 = 26639^2 + 38840^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2218181921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2218181951) 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, 256526 + ... + 265031.

It is an arithmetic number, because the mean of its divisors is an integer number (554676933).

Almost surely, 2^2218181921 is an apocalyptic number.

It is an amenable number.

2218181921 is a deficient number, since it is larger than the sum of its proper divisors (525811).

2218181921 is an equidigital number, since it uses as much as digits as its factorization.

2218181921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 525810.

The product of its digits is 4608, while the sum is 35.

The square root of 2218181921 is about 47097.5787169574. The cubic root of 2218181921 is about 1304.1645383809.

The spelling of 2218181921 in words is "two billion, two hundred eighteen million, one hundred eighty-one thousand, nine hundred twenty-one".