218947991 has 2 divisors, whose sum is σ = 218947992. Its totient is φ = 218947990.

The previous prime is 218947987. The next prime is 218948011. The reversal of 218947991 is 199749812.

218947991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 218947991 - 2² = 218947987 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (218947931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109473995 + 109473996.

It is an arithmetic number, because the mean of its divisors is an integer number (109473996).

Almost surely, 2^218947991 is an apocalyptic number.

218947991 is a deficient number, since it is larger than the sum of its proper divisors (1).

218947991 is an equidigital number, since it uses as much as digits as its factorization.

218947991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 326592, while the sum is 50.

The square root of 218947991 is about 14796.8912613427. The cubic root of 218947991 is about 602.7172965512.

The spelling of 218947991 in words is "two hundred eighteen million, nine hundred forty-seven thousand, nine hundred ninety-one".