21740 has 12 divisors (see below), whose sum is σ = 45696. Its totient is φ = 8688.

The previous prime is 21739. The next prime is 21751. The reversal of 21740 is 4712.

21740 = T₃₀ + T₃₁ + ... + T₅₃.

It is a happy number.

It is a plaindrome in base 14.

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, 524 + ... + 563.

It is an arithmetic number, because the mean of its divisors is an integer number (3808).

2²¹⁷⁴⁰ is an apocalyptic number.

21740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21740 is an abundant number, since it is smaller than the sum of its proper divisors (23956).

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 (22848).

21740 is a wasteful number, since it uses less digits than its factorization.

21740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1096 (or 1094 counting only the distinct ones).

The product of its (nonzero) digits is 56, while the sum is 14.

The square root of 21740 is about 147.4449049645. Note that the first 3 decimals coincide. The cubic root of 21740 is about 27.9095722177.

The spelling of 21740 in words is "twenty-one thousand, seven hundred forty", and thus it is an iban number.