642578721 has 4 divisors (see below), whose sum is σ = 856771632. Its totient is φ = 428385812.

The previous prime is 642578719. The next prime is 642578771. The reversal of 642578721 is 127875246.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 642578721 - 2¹ = 642578719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (642578771) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 107096451 + ... + 107096456.

It is an arithmetic number, because the mean of its divisors is an integer number (214192908).

Almost surely, 2^642578721 is an apocalyptic number.

It is an amenable number.

642578721 is a deficient number, since it is larger than the sum of its proper divisors (214192911).

642578721 is a wasteful number, since it uses less digits than its factorization.

642578721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214192910.

The product of its digits is 188160, while the sum is 42.

The square root of 642578721 is about 25349.1364941688. The cubic root of 642578721 is about 862.9297595303.

The spelling of 642578721 in words is "six hundred forty-two million, five hundred seventy-eight thousand, seven hundred twenty-one".