721990161 has 24 divisors (see below), whose sum is σ = 1057591080. Its totient is φ = 474566400.

The previous prime is 721990141. The next prime is 721990163. The reversal of 721990161 is 161099127.

It can be written as a sum of positive squares in 4 ways, for example, as 16769025 + 705221136 = 4095^2 + 26556^2 .

It is not a de Polignac number, because 721990161 - 2⁹ = 721989649 is a prime.

It is not an unprimeable number, because it can be changed into a prime (721990163) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 336151 + ... + 338291.

It is an arithmetic number, because the mean of its divisors is an integer number (44066295).

Almost surely, 2^721990161 is an apocalyptic number.

It is an amenable number.

721990161 is a deficient number, since it is larger than the sum of its proper divisors (335600919).

721990161 is a wasteful number, since it uses less digits than its factorization.

721990161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2657 (or 2654 counting only the distinct ones).

The product of its (nonzero) digits is 6804, while the sum is 36.

The square root of 721990161 is about 26869.8745996330. The cubic root of 721990161 is about 897.1059967283.

The spelling of 721990161 in words is "seven hundred twenty-one million, nine hundred ninety thousand, one hundred sixty-one".