640038921 has 12 divisors (see below), whose sum is σ = 900665712. Its totient is φ = 404234424.

The previous prime is 640038881. The next prime is 640038923. The reversal of 640038921 is 129830046.

It is not a de Polignac number, because 640038921 - 2⁹ = 640038409 is a prime.

It is not an unprimeable number, because it can be changed into a prime (640038923) 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 in 11 ways as a sum of consecutive naturals, for example, 294411 + ... + 296576.

It is an arithmetic number, because the mean of its divisors is an integer number (75055476).

Almost surely, 2^640038921 is an apocalyptic number.

It is an amenable number.

640038921 is a deficient number, since it is larger than the sum of its proper divisors (260626791).

640038921 is a wasteful number, since it uses less digits than its factorization.

640038921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 591028 (or 591009 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 33.

The square root of 640038921 is about 25298.9905134573. The cubic root of 640038921 is about 861.7913449821.

Adding to 640038921 its reverse (129830046), we get a palindrome (769868967).

The spelling of 640038921 in words is "six hundred forty million, thirty-eight thousand, nine hundred twenty-one".