21782 has 4 divisors (see below), whose sum is σ = 32676. Its totient is φ = 10890.

The previous prime is 21773. The next prime is 21787. The reversal of 21782 is 28712.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21787) by changing a digit.

21782 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5444 + ... + 5447.

It is an arithmetic number, because the mean of its divisors is an integer number (8169).

2²¹⁷⁸² is an apocalyptic number.

21782 is a deficient number, since it is larger than the sum of its proper divisors (10894).

21782 is a wasteful number, since it uses less digits than its factorization.

21782 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10893.

The product of its digits is 224, while the sum is 20.

The square root of 21782 is about 147.5872623230. The cubic root of 21782 is about 27.9275337015.

It can be divided in two parts, 2178 and 2, that multiplied together give a square (4356 = 66²).

The spelling of 21782 in words is "twenty-one thousand, seven hundred eighty-two".