21582 has 24 divisors (see below), whose sum is σ = 51480. Its totient is φ = 6480.

The previous prime is 21577. The next prime is 21587. The reversal of 21582 is 28512.

It is an interprime number because it is at equal distance from previous prime (21577) and next prime (21587).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21587) by changing a digit.

21582 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 in 11 ways as a sum of consecutive naturals, for example, 144 + ... + 252.

It is an arithmetic number, because the mean of its divisors is an integer number (2145).

2²¹⁵⁸² is an apocalyptic number.

21582 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 21582, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25740).

21582 is an abundant number, since it is smaller than the sum of its proper divisors (29898).

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

21582 is a wasteful number, since it uses less digits than its factorization.

21582 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128 (or 125 counting only the distinct ones).

The product of its digits is 160, while the sum is 18.

The square root of 21582 is about 146.9081345603. The cubic root of 21582 is about 27.8417948704.

The spelling of 21582 in words is "twenty-one thousand, five hundred eighty-two".