721665665 has 16 divisors (see below), whose sum is σ = 992200320. Its totient is φ = 493612800.

The previous prime is 721665653. The next prime is 721665671. The reversal of 721665665 is 566566127.

It is not a de Polignac number, because 721665665 - 2⁶ = 721665601 is a prime.

It is a super-3 number, since 3×721665665³ (a number of 28 digits) contains 333 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11675 + ... + 39744.

It is an arithmetic number, because the mean of its divisors is an integer number (62012520).

Almost surely, 2^721665665 is an apocalyptic number.

It is an amenable number.

721665665 is a deficient number, since it is larger than the sum of its proper divisors (270534655).

721665665 is a wasteful number, since it uses less digits than its factorization.

721665665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51832.

The product of its digits is 453600, while the sum is 44.

The square root of 721665665 is about 26863.8356345478. The cubic root of 721665665 is about 896.9715761842.

The spelling of 721665665 in words is "seven hundred twenty-one million, six hundred sixty-five thousand, six hundred sixty-five".