644680081 has 4 divisors (see below), whose sum is σ = 646288164. Its totient is φ = 643072000.

The previous prime is 644680033. The next prime is 644680109. The reversal of 644680081 is 180086446.

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 603193600 + 41486481 = 24560^2 + 6441^2 .

It is a cyclic number.

It is not a de Polignac number, because 644680081 - 2¹⁵ = 644647313 is a prime.

It is a super-2 number, since 2×644680081² = 831224813676333122, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 644680081.

It is not an unprimeable number, because it can be changed into a prime (644689081) 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, 803440 + ... + 804241.

It is an arithmetic number, because the mean of its divisors is an integer number (161572041).

Almost surely, 2^644680081 is an apocalyptic number.

It is an amenable number.

644680081 is a deficient number, since it is larger than the sum of its proper divisors (1608083).

644680081 is a wasteful number, since it uses less digits than its factorization.

644680081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1608082.

The product of its (nonzero) digits is 36864, while the sum is 37.

The square root of 644680081 is about 25390.5510180461. The cubic root of 644680081 is about 863.8693865665.

The spelling of 644680081 in words is "six hundred forty-four million, six hundred eighty thousand, eighty-one".