644661 has 12 divisors (see below), whose sum is σ = 943488. Its totient is φ = 424104.

The previous prime is 644653. The next prime is 644669. The reversal of 644661 is 166446.

It is an interprime number because it is at equal distance from previous prime (644653) and next prime (644669).

It is not a de Polignac number, because 644661 - 2³ = 644653 is a prime.

644661 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644669) 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 11 ways as a sum of consecutive naturals, for example, 316 + ... + 1178.

It is an arithmetic number, because the mean of its divisors is an integer number (78624).

2⁶⁴⁴⁶⁶¹ is an apocalyptic number.

It is an amenable number.

644661 is a deficient number, since it is larger than the sum of its proper divisors (298827).

644661 is a wasteful number, since it uses less digits than its factorization.

644661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 952 (or 949 counting only the distinct ones).

The product of its digits is 3456, while the sum is 27.

The square root of 644661 is about 802.9078402905. The cubic root of 644661 is about 86.3860863655.

The spelling of 644661 in words is "six hundred forty-four thousand, six hundred sixty-one".