644821377 has 4 divisors (see below), whose sum is σ = 859761840. Its totient is φ = 429880916.

The previous prime is 644821363. The next prime is 644821393. The reversal of 644821377 is 773128446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 644821377 - 2¹⁶ = 644755841 is a prime.

It is a super-2 number, since 2×644821377² = 831589216472352258, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644821327) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 107470227 + ... + 107470232.

It is an arithmetic number, because the mean of its divisors is an integer number (214940460).

Almost surely, 2^644821377 is an apocalyptic number.

It is an amenable number.

644821377 is a deficient number, since it is larger than the sum of its proper divisors (214940463).

644821377 is a wasteful number, since it uses less digits than its factorization.

644821377 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214940462.

The product of its digits is 225792, while the sum is 42.

The square root of 644821377 is about 25393.3333180187. Note that the first 4 decimals coincide. The cubic root of 644821377 is about 863.9324940292.

The spelling of 644821377 in words is "six hundred forty-four million, eight hundred twenty-one thousand, three hundred seventy-seven".