644263340721 has 64 divisors (see below), whose sum is σ = 1153524105216. Its totient is φ = 308895264000.

The previous prime is 644263340671. The next prime is 644263340723. The reversal of 644263340721 is 127043362446.

It is not a de Polignac number, because 644263340721 - 2²³ = 644254952113 is a prime.

It is not an unprimeable number, because it can be changed into a prime (644263340723) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 42656071 + ... + 42671171.

It is an arithmetic number, because the mean of its divisors is an integer number (18023814144).

Almost surely, 2^644263340721 is an apocalyptic number.

It is an amenable number.

644263340721 is a deficient number, since it is larger than the sum of its proper divisors (509260764495).

644263340721 is a wasteful number, since it uses less digits than its factorization.

644263340721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29342.

The product of its (nonzero) digits is 580608, while the sum is 42.

The spelling of 644263340721 in words is "six hundred forty-four billion, two hundred sixty-three million, three hundred forty thousand, seven hundred twenty-one".