21735 has 32 divisors (see below), whose sum is σ = 46080. Its totient is φ = 9504.

The previous prime is 21727. The next prime is 21737. The reversal of 21735 is 53712.

21735 is nontrivially palindromic in base 14.

It is not a de Polignac number, because 21735 - 2³ = 21727 is a prime.

21735 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21737) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 934 + ... + 956.

It is an arithmetic number, because the mean of its divisors is an integer number (1440).

2²¹⁷³⁵ is an apocalyptic number.

21735 is an abundant number, since it is smaller than the sum of its proper divisors (24345).

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 (23040).

21735 is a wasteful number, since it uses less digits than its factorization.

21735 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44 (or 38 counting only the distinct ones).

The product of its digits is 210, while the sum is 18.

The square root of 21735 is about 147.4279485037. The cubic root of 21735 is about 27.9074324054.

Adding to 21735 its product of digits (210), we get a triangular number (21945 = T₂₀₉).

It can be divided in two parts, 217 and 35, that added together give a palindrome (252).

The spelling of 21735 in words is "twenty-one thousand, seven hundred thirty-five".