644605 has 16 divisors (see below), whose sum is σ = 854784. Its totient is φ = 463680.

The previous prime is 644599. The next prime is 644617. The reversal of 644605 is 506446.

It is a happy number.

It is not a de Polignac number, because 644605 - 2³ = 644597 is a prime.

It is a Duffinian number.

644605 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 644605.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2950 + ... + 3160.

It is an arithmetic number, because the mean of its divisors is an integer number (53424).

2⁶⁴⁴⁶⁰⁵ is an apocalyptic number.

644605 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

644605 is a deficient number, since it is larger than the sum of its proper divisors (210179).

644605 is a wasteful number, since it uses less digits than its factorization.

644605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 276.

The product of its (nonzero) digits is 2880, while the sum is 25.

The square root of 644605 is about 802.8729662904. The cubic root of 644605 is about 86.3835849159.

The spelling of 644605 in words is "six hundred forty-four thousand, six hundred five".