644087816 has 8 divisors (see below), whose sum is σ = 1207664670. Its totient is φ = 322043904.

The previous prime is 644087809. The next prime is 644087861. The reversal of 644087816 is 618780446.

It can be written as a sum of positive squares in only one way, i.e., 622502500 + 21585316 = 24950^2 + 4646^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a super-2 number, since 2×644087816² = 829698229439299712, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40255481 + ... + 40255496.

Almost surely, 2^644087816 is an apocalyptic number.

It is an amenable number.

644087816 is a deficient number, since it is larger than the sum of its proper divisors (563576854).

644087816 is a wasteful number, since it uses less digits than its factorization.

644087816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80510983 (or 80510979 counting only the distinct ones).

The product of its (nonzero) digits is 258048, while the sum is 44.

The square root of 644087816 is about 25378.8852395057. The cubic root of 644087816 is about 863.6047610684.

The spelling of 644087816 in words is "six hundred forty-four million, eighty-seven thousand, eight hundred sixteen".