640550188738921 has 2 divisors, whose sum is σ = 640550188738922. Its totient is φ = 640550188738920.

The previous prime is 640550188738891. The next prime is 640550188738951. The reversal of 640550188738921 is 129837881055046.

It is a balanced prime because it is at equal distance from previous prime (640550188738891) and next prime (640550188738951).

It can be written as a sum of positive squares in only one way, i.e., 571200201042025 + 69349987696896 = 23899795^2 + 8327664^2 .

It is a cyclic number.

It is not a de Polignac number, because 640550188738921 - 2³⁷ = 640412749785449 is a prime.

It is not a weakly prime, because it can be changed into another prime (640550188738951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320275094369460 + 320275094369461.

It is an arithmetic number, because the mean of its divisors is an integer number (320275094369461).

It is a 1-persistent number, because it is pandigital, but 2⋅640550188738921 = 1281100377477842 is not.

Almost surely, 2^{640550188738921} is an apocalyptic number.

It is an amenable number.

640550188738921 is a deficient number, since it is larger than the sum of its proper divisors (1).

640550188738921 is an equidigital number, since it uses as much as digits as its factorization.

640550188738921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 116121600, while the sum is 67.

The spelling of 640550188738921 in words is "six hundred forty trillion, five hundred fifty billion, one hundred eighty-eight million, seven hundred thirty-eight thousand, nine hundred twenty-one".