640409389 has 2 divisors, whose sum is σ = 640409390. Its totient is φ = 640409388.

The previous prime is 640409359. The next prime is 640409443. The reversal of 640409389 is 983904046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 638421289 + 1988100 = 25267^2 + 1410^2 .

It is a cyclic number.

It is not a de Polignac number, because 640409389 - 2⁹ = 640408877 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640409359) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320204694 + 320204695.

It is an arithmetic number, because the mean of its divisors is an integer number (320204695).

Almost surely, 2^640409389 is an apocalyptic number.

It is an amenable number.

640409389 is a deficient number, since it is larger than the sum of its proper divisors (1).

640409389 is an equidigital number, since it uses as much as digits as its factorization.

640409389 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 186624, while the sum is 43.

The square root of 640409389 is about 25306.3112483823. The cubic root of 640409389 is about 861.9575872350.

The spelling of 640409389 in words is "six hundred forty million, four hundred nine thousand, three hundred eighty-nine".