1644 has 12 divisors (see below), whose sum is σ = 3864. Its totient is φ = 544.

The previous prime is 1637. The next prime is 1657. The reversal of 1644 is 4461.

Added to its reverse (4461) it gives a triangular number (6105 = T₁₁₀).

It is a tau number, because it is divible by the number of its divisors (12).

It is a nude number because it is divisible by every one of its digits.

1644 is a modest number, since divided by 44 gives 16 as remainder.

It is a plaindrome in base 9 and base 16.

It is a nialpdrome in base 12 and base 13.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 57 + ... + 80.

It is an arithmetic number, because the mean of its divisors is an integer number (322).

2¹⁶⁴⁴ is an apocalyptic number.

It is an amenable number.

1644 is an abundant number, since it is smaller than the sum of its proper divisors (2220).

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1932).

1644 is a wasteful number, since it uses less digits than its factorization.

1644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144 (or 142 counting only the distinct ones).

The product of its digits is 96, while the sum is 15.

The square root of 1644 is about 40.5462698654. The cubic root of 1644 is about 11.8023168868.

Adding to 1644 its reverse (4461), we get a triangular number (6105 = T₁₁₀).

It can be divided in two parts, 164 and 4, that multiplied together give a palindrome (656).

The spelling of 1644 in words is "one thousand, six hundred forty-four".