644155 has 4 divisors (see below), whose sum is σ = 772992. Its totient is φ = 515320.

The previous prime is 644153. The next prime is 644159. The reversal of 644155 is 551446.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 644155 - 2¹ = 644153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644153) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64411 + ... + 64420.

It is an arithmetic number, because the mean of its divisors is an integer number (193248).

2⁶⁴⁴¹⁵⁵ is an apocalyptic number.

644155 is a deficient number, since it is larger than the sum of its proper divisors (128837).

644155 is a wasteful number, since it uses less digits than its factorization.

644155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128836.

The product of its digits is 2400, while the sum is 25.

The square root of 644155 is about 802.5926737767. The cubic root of 644155 is about 86.3634787204.

The spelling of 644155 in words is "six hundred forty-four thousand, one hundred fifty-five".