198217721 has 8 divisors (see below), whose sum is σ = 217493640. Its totient is φ = 179517312.

The previous prime is 198217693. The next prime is 198217727. The reversal of 198217721 is 127712891.

It can be written as a sum of positive squares in 4 ways, for example, as 61795321 + 136422400 = 7861^2 + 11680^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 198217721 - 2¹⁴ = 198201337 is a prime.

It is not an unprimeable number, because it can be changed into a prime (198217727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 143156 + ... + 144533.

It is an arithmetic number, because the mean of its divisors is an integer number (27186705).

Almost surely, 2^198217721 is an apocalyptic number.

It is an amenable number.

198217721 is a deficient number, since it is larger than the sum of its proper divisors (19275919).

198217721 is a wasteful number, since it uses less digits than its factorization.

198217721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 287755.

The product of its digits is 14112, while the sum is 38.

The square root of 198217721 is about 14078.9815327672. The cubic root of 198217721 is about 583.0612233641.

The spelling of 198217721 in words is "one hundred ninety-eight million, two hundred seventeen thousand, seven hundred twenty-one".