218009979355921 has 3 divisors (see below), whose sum is σ = 218009994121083. Its totient is φ = 218009964590760.

The previous prime is 218009979355901. The next prime is 218009979356017. The reversal of 218009979355921 is 129553979900812.

The square root of 218009979355921 is 14765161.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 107220039893521 + 110789939462400 = 10354711^2 + 10525680^2 .

It is not a de Polignac number, because 218009979355921 - 2²⁷ = 218009845138193 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (218009979355901) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 7382581 + ... + 22147741.

It is an arithmetic number, because the mean of its divisors is an integer number (72669998040361).

Almost surely, 2^{218009979355921} is an apocalyptic number.

218009979355921 is the 14765161-st square number.

218009979355921 is the 7382581-st centered octagonal number.

It is an amenable number.

218009979355921 is a deficient number, since it is larger than the sum of its proper divisors (14765162).

218009979355921 is an frugal number, since it uses more digits than its factorization.

218009979355921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29530322 (or 14765161 counting only the distinct ones).

The product of its (nonzero) digits is 110224800, while the sum is 70.

The spelling of 218009979355921 in words is "two hundred eighteen trillion, nine billion, nine hundred seventy-nine million, three hundred fifty-five thousand, nine hundred twenty-one".