218821343981 has 2 divisors, whose sum is σ = 218821343982. Its totient is φ = 218821343980.

The previous prime is 218821343977. The next prime is 218821344013. The reversal of 218821343981 is 189343128812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 174668828356 + 44152515625 = 417934^2 + 210125^2 .

It is a cyclic number.

It is not a de Polignac number, because 218821343981 - 2² = 218821343977 is a prime.

It is a super-3 number, since 3×218821343981³ (a number of 35 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (218821343911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109410671990 + 109410671991.

It is an arithmetic number, because the mean of its divisors is an integer number (109410671991).

Almost surely, 2^218821343981 is an apocalyptic number.

It is an amenable number.

218821343981 is a deficient number, since it is larger than the sum of its proper divisors (1).

218821343981 is an equidigital number, since it uses as much as digits as its factorization.

218821343981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 663552, while the sum is 50.

The spelling of 218821343981 in words is "two hundred eighteen billion, eight hundred twenty-one million, three hundred forty-three thousand, nine hundred eighty-one".