640661137 has 2 divisors, whose sum is σ = 640661138. Its totient is φ = 640661136.

The previous prime is 640661129. The next prime is 640661149. The reversal of 640661137 is 731166046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 632572801 + 8088336 = 25151^2 + 2844^2 .

It is a cyclic number.

It is not a de Polignac number, because 640661137 - 2³ = 640661129 is a prime.

It is not a weakly prime, because it can be changed into another prime (640661237) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320330568 + 320330569.

It is an arithmetic number, because the mean of its divisors is an integer number (320330569).

Almost surely, 2^640661137 is an apocalyptic number.

It is an amenable number.

640661137 is a deficient number, since it is larger than the sum of its proper divisors (1).

640661137 is an equidigital number, since it uses as much as digits as its factorization.

640661137 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 18144, while the sum is 34.

The square root of 640661137 is about 25311.2847757675. The cubic root of 640661137 is about 862.0705189911.

The spelling of 640661137 in words is "six hundred forty million, six hundred sixty-one thousand, one hundred thirty-seven".