665721728 has 32 divisors (see below), whose sum is σ = 1515707760. Its totient is φ = 285308928.

The previous prime is 665721671. The next prime is 665721733. The reversal of 665721728 is 827127566.

It is a tau number, because it is divible by the number of its divisors (32).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 370601 + ... + 372392.

Almost surely, 2^665721728 is an apocalyptic number.

It is an amenable number.

665721728 is an abundant number, since it is smaller than the sum of its proper divisors (849986032).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

665721728 is an equidigital number, since it uses as much as digits as its factorization.

665721728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 743014 (or 743002 counting only the distinct ones).

The product of its digits is 282240, while the sum is 44.

The square root of 665721728 is about 25801.5838273545. The cubic root of 665721728 is about 873.1675295958.

The spelling of 665721728 in words is "six hundred sixty-five million, seven hundred twenty-one thousand, seven hundred twenty-eight".