644220 has 48 divisors (see below), whose sum is σ = 2005920. Its totient is φ = 171648.

The previous prime is 644201. The next prime is 644227. The reversal of 644220 is 22446.

644220 is a `hidden beast` number, since 644 + 2 + 20 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nialpdrome in base 10.

It is a junction number, because it is equal to n+sod(n) for n = 644193 and 644202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644227) by changing a digit.

644220 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 15 ways as a sum of consecutive naturals, for example, 57 + ... + 1136.

It is an arithmetic number, because the mean of its divisors is an integer number (41790).

2⁶⁴⁴²²⁰ is an apocalyptic number.

644220 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1002960).

644220 is an abundant number, since it is smaller than the sum of its proper divisors (1361700).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644220 is a wasteful number, since it uses less digits than its factorization.

644220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1211 (or 1203 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 644220 is about 802.6331665213. The cubic root of 644220 is about 86.3663835272.

Adding to 644220 its reverse (22446), we get a palindrome (666666).

The spelling of 644220 in words is "six hundred forty-four thousand, two hundred twenty".