640542514921 has 9 divisors (see below), whose sum is σ = 642053104599. Its totient is φ = 639035476584.

The previous prime is 640542514889. The next prime is 640542514967. The reversal of 640542514921 is 129415245046.

The square root of 640542514921 is 800339.

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

It can be written as a sum of positive squares in only one way, i.e., 483755025625 + 156787489296 = 695525^2 + 395964^2 .

It is not a de Polignac number, because 640542514921 - 2⁵ = 640542514889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640542514991) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 517818715 + ... + 517819951.

Almost surely, 2^640542514921 is an apocalyptic number.

640542514921 is the 800339-th square number.

640542514921 is the 400170-th centered octagonal number.

It is an amenable number.

640542514921 is a deficient number, since it is larger than the sum of its proper divisors (1510589678).

640542514921 is an frugal number, since it uses more digits than its factorization.

640542514921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3768 (or 1884 counting only the distinct ones).

The product of its (nonzero) digits is 345600, while the sum is 43.

Adding to 640542514921 its reverse (129415245046), we get a palindrome (769957759967).

The spelling of 640542514921 in words is "six hundred forty billion, five hundred forty-two million, five hundred fourteen thousand, nine hundred twenty-one".