21340 has 24 divisors (see below), whose sum is σ = 49392. Its totient is φ = 7680.

The previous prime is 21323. The next prime is 21341. The reversal of 21340 is 4312.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21341) by changing a digit.

21340 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 172 + ... + 268.

It is an arithmetic number, because the mean of its divisors is an integer number (2058).

2²¹³⁴⁰ is an apocalyptic number.

21340 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 21340, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24696).

21340 is an abundant number, since it is smaller than the sum of its proper divisors (28052).

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

21340 is a wasteful number, since it uses less digits than its factorization.

21340 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117 (or 115 counting only the distinct ones).

The product of its (nonzero) digits is 24, while the sum is 10.

The square root of 21340 is about 146.0821686586. The cubic root of 21340 is about 27.7373396784.

Subtracting from 21340 its product of nonzero digits (24), we obtain a square (21316 = 146²).

Adding to 21340 its reverse (4312), we get a palindrome (25652).

It can be divided in two parts, 213 and 40, that added together give a triangular number (253 = T₂₂).

The spelling of 21340 in words is "twenty-one thousand, three hundred forty", and thus it is an iban number.