640697923 has 2 divisors, whose sum is σ = 640697924. Its totient is φ = 640697922.

The previous prime is 640697903. The next prime is 640697947. The reversal of 640697923 is 329796046.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640697923 is a prime.

It is not a weakly prime, because it can be changed into another prime (640697903) 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, 320348961 + 320348962.

It is an arithmetic number, because the mean of its divisors is an integer number (320348962).

Almost surely, 2^640697923 is an apocalyptic number.

640697923 is a deficient number, since it is larger than the sum of its proper divisors (1).

640697923 is an equidigital number, since it uses as much as digits as its factorization.

640697923 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 489888, while the sum is 46.

The square root of 640697923 is about 25312.0114372604. The cubic root of 640697923 is about 862.0870183630.

It can be divided in two parts, 6406 and 97923, that added together give a square (104329 = 323²).

The spelling of 640697923 in words is "six hundred forty million, six hundred ninety-seven thousand, nine hundred twenty-three".