640691441 has 4 divisors (see below), whose sum is σ = 689975412. Its totient is φ = 591407472.

The previous prime is 640691437. The next prime is 640691459. The reversal of 640691441 is 144196046.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 127215841 + 513475600 = 11279^2 + 22660^2 .

It is a cyclic number.

It is not a de Polignac number, because 640691441 - 2² = 640691437 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640691041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 24641966 + ... + 24641991.

It is an arithmetic number, because the mean of its divisors is an integer number (172493853).

Almost surely, 2^640691441 is an apocalyptic number.

It is an amenable number.

640691441 is a deficient number, since it is larger than the sum of its proper divisors (49283971).

640691441 is a wasteful number, since it uses less digits than its factorization.

640691441 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49283970.

The product of its (nonzero) digits is 20736, while the sum is 35.

The square root of 640691441 is about 25311.8833949590. The cubic root of 640691441 is about 862.0841110819.

The spelling of 640691441 in words is "six hundred forty million, six hundred ninety-one thousand, four hundred forty-one".