640978940 has 96 divisors (see below), whose sum is σ = 1603252224. Its totient is φ = 210631680.

The previous prime is 640978937. The next prime is 640978957. The reversal of 640978940 is 49879046.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 489767 + ... + 491073.

It is an arithmetic number, because the mean of its divisors is an integer number (16700544).

Almost surely, 2^640978940 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 640978940, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (801626112).

640978940 is an abundant number, since it is smaller than the sum of its proper divisors (962273284).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

640978940 is a wasteful number, since it uses less digits than its factorization.

640978940 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1467 (or 1465 counting only the distinct ones).

The product of its (nonzero) digits is 435456, while the sum is 47.

The square root of 640978940 is about 25317.5618889339. The cubic root of 640978940 is about 862.2130401528.

It can be divided in two parts, 64097 and 8940, that added together give a palindrome (73037).

The spelling of 640978940 in words is "six hundred forty million, nine hundred seventy-eight thousand, nine hundred forty".