640040440021 has 2 divisors, whose sum is σ = 640040440022. Its totient is φ = 640040440020.

The previous prime is 640040439989. The next prime is 640040440099. The reversal of 640040440021 is 120044040046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 577735287921 + 62305152100 = 760089^2 + 249610^2 .

It is a cyclic number.

It is not a de Polignac number, because 640040440021 - 2⁵ = 640040439989 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640040440421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320020220010 + 320020220011.

It is an arithmetic number, because the mean of its divisors is an integer number (320020220011).

Almost surely, 2^640040440021 is an apocalyptic number.

It is an amenable number.

640040440021 is a deficient number, since it is larger than the sum of its proper divisors (1).

640040440021 is an equidigital number, since it uses as much as digits as its factorization.

640040440021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3072, while the sum is 25.

Adding to 640040440021 its reverse (120044040046), we get a palindrome (760084480067).

The spelling of 640040440021 in words is "six hundred forty billion, forty million, four hundred forty thousand, twenty-one".