644733657 has 12 divisors (see below), whose sum is σ = 933681060. Its totient is φ = 428715168.

The previous prime is 644733643. The next prime is 644733667. The reversal of 644733657 is 756337446.

It can be written as a sum of positive squares in 2 ways, for example, as 273439296 + 371294361 = 16536^2 + 19269^2 .

It is not a de Polignac number, because 644733657 - 2⁴ = 644733641 is a prime.

It is not an unprimeable number, because it can be changed into a prime (644733667) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 88578 + ... + 95579.

It is an arithmetic number, because the mean of its divisors is an integer number (77806755).

Almost surely, 2^644733657 is an apocalyptic number.

It is an amenable number.

644733657 is a deficient number, since it is larger than the sum of its proper divisors (288947403).

644733657 is a wasteful number, since it uses less digits than its factorization.

644733657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 184552 (or 184549 counting only the distinct ones).

The product of its digits is 1270080, while the sum is 45.

The square root of 644733657 is about 25391.6060342783. The cubic root of 644733657 is about 863.8933164637.

It can be divided in two parts, 6447 and 33657, that added together give a palindrome (40104).

The spelling of 644733657 in words is "six hundred forty-four million, seven hundred thirty-three thousand, six hundred fifty-seven".