646721680 has 40 divisors (see below), whose sum is σ = 1640323584. Its totient is φ = 235171200.

The previous prime is 646721651. The next prime is 646721707. The reversal of 646721680 is 86127646.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 366576 + ... + 368335.

Almost surely, 2^646721680 is an apocalyptic number.

It is an amenable number.

646721680 is an abundant number, since it is smaller than the sum of its proper divisors (993601904).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

646721680 is a wasteful number, since it uses less digits than its factorization.

646721680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 734935 (or 734929 counting only the distinct ones).

The product of its (nonzero) digits is 96768, while the sum is 40.

The square root of 646721680 is about 25430.7231513380. The cubic root of 646721680 is about 864.7803378209.

The spelling of 646721680 in words is "six hundred forty-six million, seven hundred twenty-one thousand, six hundred eighty".