6440 has 32 divisors (see below), whose sum is σ = 17280. Its totient is φ = 2112.

The previous prime is 6427. The next prime is 6449. The reversal of 6440 is 446.

6440 = T₂₀ + T₂₁ + ... + T₃₅.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (14).

It is a plaindrome in base 12.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6449) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 269 + ... + 291.

It is an arithmetic number, because the mean of its divisors is an integer number (540).

2⁶⁴⁴⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (8640).

6440 is an abundant number, since it is smaller than the sum of its proper divisors (10840).

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

6440 is a wasteful number, since it uses less digits than its factorization.

6440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41 (or 37 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 14.

The square root of 6440 is about 80.2496105910. The cubic root of 6440 is about 18.6049549369.

Adding to 6440 its reverse (446), we get a palindrome (6886).

The spelling of 6440 in words is "six thousand, four hundred forty".