643781600721 has 12 divisors (see below), whose sum is σ = 1062750579072. Its totient is φ = 367875200376.

The previous prime is 643781600711. The next prime is 643781600731. The reversal of 643781600721 is 127006187346.

643781600721 is a `hidden beast` number, since 6 + 4 + 37 + 8 + 1 + 600 + 7 + 2 + 1 = 666.

It is an interprime number because it is at equal distance from previous prime (643781600711) and next prime (643781600731).

It is not a de Polignac number, because 643781600721 - 2¹⁰ = 643781599697 is a prime.

It is not an unprimeable number, because it can be changed into a prime (643781600711) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5109377721 + ... + 5109377846.

It is an arithmetic number, because the mean of its divisors is an integer number (88562548256).

Almost surely, 2^643781600721 is an apocalyptic number.

It is an amenable number.

643781600721 is a deficient number, since it is larger than the sum of its proper divisors (418968978351).

643781600721 is a wasteful number, since it uses less digits than its factorization.

643781600721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10218755580 (or 10218755577 counting only the distinct ones).

The product of its (nonzero) digits is 338688, while the sum is 45.

The spelling of 643781600721 in words is "six hundred forty-three billion, seven hundred eighty-one million, six hundred thousand, seven hundred twenty-one".