218981681 has 2 divisors, whose sum is σ = 218981682. Its totient is φ = 218981680.

The previous prime is 218981663. The next prime is 218981717. The reversal of 218981681 is 186189812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 115756081 + 103225600 = 10759^2 + 10160^2 .

It is a cyclic number.

It is not a de Polignac number, because 218981681 - 2⁶ = 218981617 is a prime.

It is a super-2 number, since 2×218981681² = 95905953227171522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (218981611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109490840 + 109490841.

It is an arithmetic number, because the mean of its divisors is an integer number (109490841).

Almost surely, 2^218981681 is an apocalyptic number.

It is an amenable number.

218981681 is a deficient number, since it is larger than the sum of its proper divisors (1).

218981681 is an equidigital number, since it uses as much as digits as its factorization.

218981681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 55296, while the sum is 44.

The square root of 218981681 is about 14798.0296323531. The cubic root of 218981681 is about 602.7482087696.

The spelling of 218981681 in words is "two hundred eighteen million, nine hundred eighty-one thousand, six hundred eighty-one".