640616561 has 8 divisors (see below), whose sum is σ = 690888744. Its totient is φ = 590486400.

The previous prime is 640616551. The next prime is 640616563. The reversal of 640616561 is 165616046.

It can be written as a sum of positive squares in 4 ways, for example, as 163456225 + 477160336 = 12785^2 + 21844^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 640616561 - 2⁶ = 640616497 is a prime.

It is not an unprimeable number, because it can be changed into a prime (640616563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 26036 + ... + 44261.

It is an arithmetic number, because the mean of its divisors is an integer number (86361093).

Almost surely, 2^640616561 is an apocalyptic number.

It is an amenable number.

640616561 is a deficient number, since it is larger than the sum of its proper divisors (50272183).

640616561 is a wasteful number, since it uses less digits than its factorization.

640616561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71011.

The product of its (nonzero) digits is 25920, while the sum is 35.

The square root of 640616561 is about 25310.4042045954. The cubic root of 640616561 is about 862.0505247776.

The spelling of 640616561 in words is "six hundred forty million, six hundred sixteen thousand, five hundred sixty-one".