642728721 has 16 divisors (see below), whose sum is σ = 911108736. Its totient is φ = 402120576.

The previous prime is 642728717. The next prime is 642728731. The reversal of 642728721 is 127827246.

It is not a de Polignac number, because 642728721 - 2² = 642728717 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 642728721.

It is not an unprimeable number, because it can be changed into a prime (642728731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 84220 + ... + 91533.

It is an arithmetic number, because the mean of its divisors is an integer number (56944296).

Almost surely, 2^642728721 is an apocalyptic number.

It is an amenable number.

642728721 is a deficient number, since it is larger than the sum of its proper divisors (268380015).

642728721 is a wasteful number, since it uses less digits than its factorization.

642728721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 175832.

The product of its digits is 75264, while the sum is 39.

The square root of 642728721 is about 25352.0950021887. The cubic root of 642728721 is about 862.9969001463.

The spelling of 642728721 in words is "six hundred forty-two million, seven hundred twenty-eight thousand, seven hundred twenty-one".