721904161 has 24 divisors (see below), whose sum is σ = 831641472. Its totient is φ = 621165600.

The previous prime is 721904137. The next prime is 721904177. The reversal of 721904161 is 161409127.

It is not a de Polignac number, because 721904161 - 2⁵ = 721904129 is a prime.

It is a super-2 number, since 2×721904161² = 1042291235338227842, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (721904111) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 496111 + ... + 497563.

It is an arithmetic number, because the mean of its divisors is an integer number (34651728).

Almost surely, 2^721904161 is an apocalyptic number.

It is an amenable number.

721904161 is a deficient number, since it is larger than the sum of its proper divisors (109737311).

721904161 is a wasteful number, since it uses less digits than its factorization.

721904161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1573 (or 1542 counting only the distinct ones).

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 721904161 is about 26868.2742467766. The cubic root of 721904161 is about 897.0703756615.

The spelling of 721904161 in words is "seven hundred twenty-one million, nine hundred four thousand, one hundred sixty-one".