218871721 has 4 divisors (see below), whose sum is σ = 222459844. Its totient is φ = 215283600.

The previous prime is 218871707. The next prime is 218871733. The reversal of 218871721 is 127178812.

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 21160000 + 197711721 = 4600^2 + 14061^2 .

It is a cyclic number.

It is not a de Polignac number, because 218871721 - 2¹³ = 218863529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (218871701) 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, 1793970 + ... + 1794091.

It is an arithmetic number, because the mean of its divisors is an integer number (55614961).

Almost surely, 2^218871721 is an apocalyptic number.

It is an amenable number.

218871721 is a deficient number, since it is larger than the sum of its proper divisors (3588123).

218871721 is an equidigital number, since it uses as much as digits as its factorization.

218871721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3588122.

The product of its digits is 12544, while the sum is 37.

The square root of 218871721 is about 14794.3138063244. The cubic root of 218871721 is about 602.6473033886.

The spelling of 218871721 in words is "two hundred eighteen million, eight hundred seventy-one thousand, seven hundred twenty-one".