640449678961 has 3 divisors (see below), whose sum is σ = 640450479243. Its totient is φ = 640448878680.

The previous prime is 640449678949. The next prime is 640449678989. The reversal of 640449678961 is 169876944046.

The square root of 640449678961 is 800281.

It is a perfect power (a square), and thus also a powerful number.

640449678961 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 620126325361 + 20323353600 = 787481^2 + 142560^2 .

It is not a de Polignac number, because 640449678961 - 2⁷ = 640449678833 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 640449678893 and 640449678902.

It is not an unprimeable number, because it can be changed into a prime (640449676961) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 400141 + ... + 1200421.

It is an arithmetic number, because the mean of its divisors is an integer number (213483493081).

Almost surely, 2^640449678961 is an apocalyptic number.

640449678961 is the 800281-st square number.

640449678961 is the 400141-st centered octagonal number.

It is an amenable number.

640449678961 is a deficient number, since it is larger than the sum of its proper divisors (800282).

640449678961 is an frugal number, since it uses more digits than its factorization.

640449678961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1600562 (or 800281 counting only the distinct ones).

The product of its (nonzero) digits is 62705664, while the sum is 64.

Multiplying 640449678961 by its sum of digits (64), we get a square (40988779453504 = 6402248²).

The spelling of 640449678961 in words is "six hundred forty billion, four hundred forty-nine million, six hundred seventy-eight thousand, nine hundred sixty-one".