21743 has 4 divisors (see below), whose sum is σ = 23040. Its totient is φ = 20448.

The previous prime is 21739. The next prime is 21751. The reversal of 21743 is 34712.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21743 - 2² = 21739 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (17), and also a Moran number because the ratio is a prime number: 1279 = 21743 / (2 + 1 + 7 + 4 + 3).

It is a d-powerful number, because it can be written as 2¹¹ + 1 + 7 + 4 + 3⁹ .

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21713) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 623 + ... + 656.

It is an arithmetic number, because the mean of its divisors is an integer number (5760).

2²¹⁷⁴³ is an apocalyptic number.

21743 is a deficient number, since it is larger than the sum of its proper divisors (1297).

21743 is a wasteful number, since it uses less digits than its factorization.

21743 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1296.

The product of its digits is 168, while the sum is 17.

The square root of 21743 is about 147.4550779051. The cubic root of 21743 is about 27.9108559476.

It can be divided in two parts, 2 and 1743, that multiplied together give a triangular number (3486 = T₈₃).

The spelling of 21743 in words is "twenty-one thousand, seven hundred forty-three", and thus it is an iban number.