640981968 has 40 divisors (see below), whose sum is σ = 1806405216. Its totient is φ = 194236800.

The previous prime is 640981949. The next prime is 640981981. The reversal of 640981968 is 869189046.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 640981968.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 606463 + ... + 607518.

Almost surely, 2^640981968 is an apocalyptic number.

It is an amenable number.

640981968 is an abundant number, since it is smaller than the sum of its proper divisors (1165423248).

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

640981968 is a wasteful number, since it uses less digits than its factorization.

640981968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1214003 (or 1213997 counting only the distinct ones).

The product of its (nonzero) digits is 746496, while the sum is 51.

The square root of 640981968 is about 25317.6216892504. The cubic root of 640981968 is about 862.2143978557.

It can be divided in two parts, 64098 and 1968, that added together give a palindrome (66066).

The spelling of 640981968 in words is "six hundred forty million, nine hundred eighty-one thousand, nine hundred sixty-eight".