218923921 has 2 divisors, whose sum is σ = 218923922. Its totient is φ = 218923920.

The previous prime is 218923919. The next prime is 218923927. The reversal of 218923921 is 129329812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 183223296 + 35700625 = 13536^2 + 5975^2 .

It is a cyclic number.

It is not a de Polignac number, because 218923921 - 2¹ = 218923919 is a prime.

Together with 218923919, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (218923927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109461960 + 109461961.

It is an arithmetic number, because the mean of its divisors is an integer number (109461961).

Almost surely, 2^218923921 is an apocalyptic number.

It is an amenable number.

218923921 is a deficient number, since it is larger than the sum of its proper divisors (1).

218923921 is an equidigital number, since it uses as much as digits as its factorization.

218923921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15552, while the sum is 37.

The square root of 218923921 is about 14796.0778924687. The cubic root of 218923921 is about 602.6952092100.

The spelling of 218923921 in words is "two hundred eighteen million, nine hundred twenty-three thousand, nine hundred twenty-one".