218211221 has 2 divisors, whose sum is σ = 218211222. Its totient is φ = 218211220.

The previous prime is 218211211. The next prime is 218211239. The reversal of 218211221 is 122112812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 193071025 + 25140196 = 13895^2 + 5014^2 .

It is a cyclic number.

It is not a de Polignac number, because 218211221 - 2¹⁸ = 217949077 is a prime.

It is a super-2 number, since 2×218211221² = 95232273940621682, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 218211193 and 218211202.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (218211211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109105610 + 109105611.

It is an arithmetic number, because the mean of its divisors is an integer number (109105611).

Almost surely, 2^218211221 is an apocalyptic number.

It is an amenable number.

218211221 is a deficient number, since it is larger than the sum of its proper divisors (1).

218211221 is an equidigital number, since it uses as much as digits as its factorization.

218211221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 128, while the sum is 20.

The square root of 218211221 is about 14771.9741740906. The cubic root of 218211221 is about 602.0404797230.

The spelling of 218211221 in words is "two hundred eighteen million, two hundred eleven thousand, two hundred twenty-one".