21580 has 24 divisors (see below), whose sum is σ = 49392. Its totient is φ = 7872.

The previous prime is 21577. The next prime is 21587. The reversal of 21580 is 8512.

21580 = T₅₁ + T₅₂ + ... + T₆₃.

It is a happy number.

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

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 219 + ... + 301.

It is an arithmetic number, because the mean of its divisors is an integer number (2058).

2²¹⁵⁸⁰ is an apocalyptic number.

21580 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21580, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24696).

21580 is an abundant number, since it is smaller than the sum of its proper divisors (27812).

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

21580 is a wasteful number, since it uses less digits than its factorization.

21580 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 105 (or 103 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21580 is about 146.9013274276. The cubic root of 21580 is about 27.8409348125.

It can be divided in two parts, 2 and 1580, that multiplied together give a triangular number (3160 = T₇₉).

The spelling of 21580 in words is "twenty-one thousand, five hundred eighty".