640533661 has 2 divisors, whose sum is σ = 640533662. Its totient is φ = 640533660.

The previous prime is 640533631. The next prime is 640533683. The reversal of 640533661 is 166335046.

640533661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 406627225 + 233906436 = 20165^2 + 15294^2 .

It is a cyclic number.

It is not a de Polignac number, because 640533661 - 2⁵ = 640533629 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640533631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320266830 + 320266831.

It is an arithmetic number, because the mean of its divisors is an integer number (320266831).

Almost surely, 2^640533661 is an apocalyptic number.

It is an amenable number.

640533661 is a deficient number, since it is larger than the sum of its proper divisors (1).

640533661 is an equidigital number, since it uses as much as digits as its factorization.

640533661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 38880, while the sum is 34.

The square root of 640533661 is about 25308.7664851529. The cubic root of 640533661 is about 862.0133381693.

The spelling of 640533661 in words is "six hundred forty million, five hundred thirty-three thousand, six hundred sixty-one".