199978001721 has 27 divisors (see below), whose sum is σ = 302008761327. Its totient is φ = 127502527680.

The previous prime is 199978001701. The next prime is 199978001731. The reversal of 199978001721 is 127100879991.

The square root of 199978001721 is 447189.

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

It can be written as a sum of positive squares in only one way, i.e., 190105592121 + 9872409600 = 436011^2 + 99360^2 .

It is not a de Polignac number, because 199978001721 - 2¹³ = 199977993529 is a prime.

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (199978001701) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 30852801 + ... + 30859281.

Almost surely, 2^199978001721 is an apocalyptic number.

199978001721 is the 447189-th square number.

199978001721 is the 223595-th centered octagonal number.

It is an amenable number.

199978001721 is a deficient number, since it is larger than the sum of its proper divisors (102030759606).

199978001721 is an frugal number, since it uses more digits than its factorization.

199978001721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13014 (or 6507 counting only the distinct ones).

The product of its (nonzero) digits is 571536, while the sum is 54.

The spelling of 199978001721 in words is "one hundred ninety-nine billion, nine hundred seventy-eight million, one thousand, seven hundred twenty-one".