218221921 has 2 divisors, whose sum is σ = 218221922. Its totient is φ = 218221920.

The previous prime is 218221909. The next prime is 218221931. The reversal of 218221921 is 129122812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 192099600 + 26122321 = 13860^2 + 5111^2 .

It is a cyclic number.

It is not a de Polignac number, because 218221921 - 2⁵ = 218221889 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 218221921.

It is not a weakly prime, because it can be changed into another prime (218221931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109110960 + 109110961.

It is an arithmetic number, because the mean of its divisors is an integer number (109110961).

Almost surely, 2^218221921 is an apocalyptic number.

It is an amenable number.

218221921 is a deficient number, since it is larger than the sum of its proper divisors (1).

218221921 is an equidigital number, since it uses as much as digits as its factorization.

218221921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1152, while the sum is 28.

The square root of 218221921 is about 14772.3363419603. The cubic root of 218221921 is about 602.0503199256.

The spelling of 218221921 in words is "two hundred eighteen million, two hundred twenty-one thousand, nine hundred twenty-one".