640438109 has 2 divisors, whose sum is σ = 640438110. Its totient is φ = 640438108.

The previous prime is 640438103. The next prime is 640438177. The reversal of 640438109 is 901834046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 625150009 + 15288100 = 25003^2 + 3910^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640438109 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640438103) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320219054 + 320219055.

It is an arithmetic number, because the mean of its divisors is an integer number (320219055).

Almost surely, 2^640438109 is an apocalyptic number.

It is an amenable number.

640438109 is a deficient number, since it is larger than the sum of its proper divisors (1).

640438109 is an equidigital number, since it uses as much as digits as its factorization.

640438109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 20736, while the sum is 35.

The square root of 640438109 is about 25306.8786893998. The cubic root of 640438109 is about 861.9704722490.

The spelling of 640438109 in words is "six hundred forty million, four hundred thirty-eight thousand, one hundred nine".