644646397 has 4 divisors (see below), whose sum is σ = 646254396. Its totient is φ = 643038400.

The previous prime is 644646361. The next prime is 644646413. The reversal of 644646397 is 793646446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 793646446 = 2 ⋅396823223.

It can be written as a sum of positive squares in 2 ways, for example, as 448338276 + 196308121 = 21174^2 + 14011^2 .

It is a cyclic number.

It is not a de Polignac number, because 644646397 - 2¹⁹ = 644122109 is a prime.

It is a super-3 number, since 3×644646397³ (a number of 27 digits) contains 333 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 644646397.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644646347) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 803398 + ... + 804199.

It is an arithmetic number, because the mean of its divisors is an integer number (161563599).

Almost surely, 2^644646397 is an apocalyptic number.

It is an amenable number.

644646397 is a deficient number, since it is larger than the sum of its proper divisors (1607999).

644646397 is a wasteful number, since it uses less digits than its factorization.

644646397 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1607998.

The product of its digits is 2612736, while the sum is 49.

The square root of 644646397 is about 25389.8876917563. The cubic root of 644646397 is about 863.8543408179.

Adding to 644646397 its sum of digits (49), we get a palindrome (644646446).

The spelling of 644646397 in words is "six hundred forty-four million, six hundred forty-six thousand, three hundred ninety-seven".