640691440 has 20 divisors (see below), whose sum is σ = 1489607784. Its totient is φ = 256276544.

The previous prime is 640691437. The next prime is 640691459. The reversal of 640691440 is 44196046.

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 640691396 and 640691405.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4004242 + ... + 4004401.

Almost surely, 2^640691440 is an apocalyptic number.

It is an amenable number.

640691440 is an abundant number, since it is smaller than the sum of its proper divisors (848916344).

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

640691440 is a wasteful number, since it uses less digits than its factorization.

640691440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8008656 (or 8008650 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 34.

The square root of 640691440 is about 25311.8833752054. The cubic root of 640691440 is about 862.0841106334.

The spelling of 640691440 in words is "six hundred forty million, six hundred ninety-one thousand, four hundred forty".