19898205721 has 3 divisors (see below), whose sum is σ = 19898346783. Its totient is φ = 19898064660.

The previous prime is 19898205709. The next prime is 19898205737. The reversal of 19898205721 is 12750289891.

The square root of 19898205721 is 141061.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12750289891 = 19 ⋅671067889.

It can be written as a sum of positive squares in only one way, i.e., 17229450121 + 2668755600 = 131261^2 + 51660^2 .

It is not a de Polignac number, because 19898205721 - 2⁹ = 19898205209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19898205121) 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, 70531 + ... + 211591.

It is an arithmetic number, because the mean of its divisors is an integer number (6632782261).

Almost surely, 2^19898205721 is an apocalyptic number.

19898205721 is the 141061-st square number.

19898205721 is the 70531-st centered octagonal number.

It is an amenable number.

19898205721 is a deficient number, since it is larger than the sum of its proper divisors (141062).

19898205721 is an frugal number, since it uses more digits than its factorization.

19898205721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 282122 (or 141061 counting only the distinct ones).

The product of its (nonzero) digits is 725760, while the sum is 52.

The spelling of 19898205721 in words is "nineteen billion, eight hundred ninety-eight million, two hundred five thousand, seven hundred twenty-one".