640691437 has 2 divisors, whose sum is σ = 640691438. Its totient is φ = 640691436.

The previous prime is 640691423. The next prime is 640691459. The reversal of 640691437 is 734196046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 528034441 + 112656996 = 22979^2 + 10614^2 .

It is a cyclic number.

It is not a de Polignac number, because 640691437 - 2⁷ = 640691309 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 640691437.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640694437) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320345718 + 320345719.

It is an arithmetic number, because the mean of its divisors is an integer number (320345719).

Almost surely, 2^640691437 is an apocalyptic number.

It is an amenable number.

640691437 is a deficient number, since it is larger than the sum of its proper divisors (1).

640691437 is an equidigital number, since it uses as much as digits as its factorization.

640691437 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 108864, while the sum is 40.

The square root of 640691437 is about 25311.8833159447. The cubic root of 640691437 is about 862.0841092879.

The spelling of 640691437 in words is "six hundred forty million, six hundred ninety-one thousand, four hundred thirty-seven".