640423961 has 2 divisors, whose sum is σ = 640423962. Its totient is φ = 640423960.

The previous prime is 640423957. The next prime is 640423991. The reversal of 640423961 is 169324046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 623251225 + 17172736 = 24965^2 + 4144^2 .

It is a cyclic number.

It is not a de Polignac number, because 640423961 - 2² = 640423957 is a prime.

It is not a weakly prime, because it can be changed into another prime (640423991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320211980 + 320211981.

It is an arithmetic number, because the mean of its divisors is an integer number (320211981).

Almost surely, 2^640423961 is an apocalyptic number.

It is an amenable number.

640423961 is a deficient number, since it is larger than the sum of its proper divisors (1).

640423961 is an equidigital number, since it uses as much as digits as its factorization.

640423961 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 31104, while the sum is 35.

The square root of 640423961 is about 25306.5991591126. The cubic root of 640423961 is about 861.9641249023.

The spelling of 640423961 in words is "six hundred forty million, four hundred twenty-three thousand, nine hundred sixty-one".