644747805 has 144 divisors (see below), whose sum is σ = 1318052736. Its totient is φ = 289578240.

The previous prime is 644747801. The next prime is 644747819. The reversal of 644747805 is 508747446.

It is not a de Polignac number, because 644747805 - 2² = 644747801 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644747801) by changing a digit.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 9080920 + ... + 9080990.

It is an arithmetic number, because the mean of its divisors is an integer number (9153144).

Almost surely, 2^644747805 is an apocalyptic number.

644747805 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

644747805 is an abundant number, since it is smaller than the sum of its proper divisors (673304931).

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

644747805 is a wasteful number, since it uses less digits than its factorization.

644747805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 176 (or 154 counting only the distinct ones).

The product of its (nonzero) digits is 752640, while the sum is 45.

The square root of 644747805 is about 25391.8846287549. The cubic root of 644747805 is about 863.8996354933.

The spelling of 644747805 in words is "six hundred forty-four million, seven hundred forty-seven thousand, eight hundred five".