218129921 has 4 divisors (see below), whose sum is σ = 218204244. Its totient is φ = 218055600.

The previous prime is 218129917. The next prime is 218129939. The reversal of 218129921 is 129921812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 164839921 + 53290000 = 12839^2 + 7300^2 .

It is a cyclic number.

It is not a de Polignac number, because 218129921 - 2² = 218129917 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (218129971) 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, 32570 + ... + 38691.

It is an arithmetic number, because the mean of its divisors is an integer number (54551061).

Almost surely, 2^218129921 is an apocalyptic number.

It is an amenable number.

218129921 is a deficient number, since it is larger than the sum of its proper divisors (74323).

218129921 is an equidigital number, since it uses as much as digits as its factorization.

218129921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74322.

The product of its digits is 5184, while the sum is 35.

The square root of 218129921 is about 14769.2220851337. Note that the first 3 decimals coincide. The cubic root of 218129921 is about 601.9657020669.

The spelling of 218129921 in words is "two hundred eighteen million, one hundred twenty-nine thousand, nine hundred twenty-one".