640644656545 has 16 divisors (see below), whose sum is σ = 769920238080. Its totient is φ = 511751862144.

The previous prime is 640644656543. The next prime is 640644656557. The reversal of 640644656545 is 545656446046.

It is a cyclic number.

It is not a de Polignac number, because 640644656545 - 2¹ = 640644656543 is a prime.

It is a super-2 number, since 2×640644656545² (a number of 24 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (640644656543) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9312886 + ... + 9381424.

It is an arithmetic number, because the mean of its divisors is an integer number (48120014880).

Almost surely, 2^640644656545 is an apocalyptic number.

It is an amenable number.

640644656545 is a deficient number, since it is larger than the sum of its proper divisors (129275581535).

640644656545 is a wasteful number, since it uses less digits than its factorization.

640644656545 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71304.

The product of its (nonzero) digits is 41472000, while the sum is 55.

The spelling of 640644656545 in words is "six hundred forty billion, six hundred forty-four million, six hundred fifty-six thousand, five hundred forty-five".