218421993 has 4 divisors (see below), whose sum is σ = 291229328. Its totient is φ = 145614660.

The previous prime is 218421991. The next prime is 218422003. The reversal of 218421993 is 399124812.

218421993 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 218421993 - 2¹ = 218421991 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (218421991) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36403663 + ... + 36403668.

It is an arithmetic number, because the mean of its divisors is an integer number (72807332).

Almost surely, 2^218421993 is an apocalyptic number.

It is an amenable number.

218421993 is a deficient number, since it is larger than the sum of its proper divisors (72807335).

218421993 is an equidigital number, since it uses as much as digits as its factorization.

218421993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72807334.

The product of its digits is 31104, while the sum is 39.

The square root of 218421993 is about 14779.1066374122. The cubic root of 218421993 is about 602.2342559513.

The spelling of 218421993 in words is "two hundred eighteen million, four hundred twenty-one thousand, nine hundred ninety-three".