721665451 has 4 divisors (see below), whose sum is σ = 777178192. Its totient is φ = 666152712.

The previous prime is 721665433. The next prime is 721665463. The reversal of 721665451 is 154566127.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 721665451 - 2⁷ = 721665323 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 721665451.

It is not an unprimeable number, because it can be changed into a prime (721665751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27756351 + ... + 27756376.

It is an arithmetic number, because the mean of its divisors is an integer number (194294548).

Almost surely, 2^721665451 is an apocalyptic number.

721665451 is a deficient number, since it is larger than the sum of its proper divisors (55512741).

721665451 is a wasteful number, since it uses less digits than its factorization.

721665451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55512740.

The product of its digits is 50400, while the sum is 37.

The square root of 721665451 is about 26863.8316514975. The cubic root of 721665451 is about 896.9714875227.

The spelling of 721665451 in words is "seven hundred twenty-one million, six hundred sixty-five thousand, four hundred fifty-one".