644640802 has 32 divisors (see below), whose sum is σ = 1078524720. Its totient is φ = 287089920.

The previous prime is 644640793. The next prime is 644640809. The reversal of 644640802 is 208046446.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 255328441 + 389312361 = 15979^2 + 19731^2 .

It is not an unprimeable number, because it can be changed into a prime (644640809) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 80224 + ... + 87892.

Almost surely, 2^644640802 is an apocalyptic number.

644640802 is a deficient number, since it is larger than the sum of its proper divisors (433883918).

644640802 is a wasteful number, since it uses less digits than its factorization.

644640802 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7798.

The product of its (nonzero) digits is 36864, while the sum is 34.

The square root of 644640802 is about 25389.7775098562. Note that the first 3 decimals coincide. The cubic root of 644640802 is about 863.8518416292.

The spelling of 644640802 in words is "six hundred forty-four million, six hundred forty thousand, eight hundred two".