20440 has 32 divisors (see below), whose sum is σ = 53280. Its totient is φ = 6912.

The previous prime is 20431. The next prime is 20441. The reversal of 20440 is 4402.

20440 = 51² + 52² + ... + 57².

20440 is nontrivially palindromic in base 3.

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a nialpdrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20441) by changing a digit.

20440 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a nontrivial repunit in base 27.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 244 + ... + 316.

It is an arithmetic number, because the mean of its divisors is an integer number (1665).

2²⁰⁴⁴⁰ is an apocalyptic number.

20440 is a gapful number since it is divisible by the number (20) 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 20440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26640).

20440 is an abundant number, since it is smaller than the sum of its proper divisors (32840).

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

20440 is a wasteful number, since it uses less digits than its factorization.

20440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91 (or 87 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 10.

The square root of 20440 is about 142.9685280053. The cubic root of 20440 is about 27.3417912883.

Adding to 20440 its reverse (4402), we get a palindrome (24842).

The spelling of 20440 in words is "twenty thousand, four hundred forty", and thus it is an iban number.