21860 has 12 divisors (see below), whose sum is σ = 45948. Its totient is φ = 8736.

The previous prime is 21859. The next prime is 21863. The reversal of 21860 is 6812.

21860 = T₉₁ + T₉₂ + ... + T₉₅.

It can be written as a sum of positive squares in 2 ways, for example, as 16384 + 5476 = 128^2 + 74^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21863) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 527 + ... + 566.

It is an arithmetic number, because the mean of its divisors is an integer number (3829).

2²¹⁸⁶⁰ is an apocalyptic number.

21860 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21860 is an abundant number, since it is smaller than the sum of its proper divisors (24088).

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 (22974).

21860 is a wasteful number, since it uses less digits than its factorization.

21860 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1102 (or 1100 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 21860 is about 147.8512766262. The cubic root of 21860 is about 27.9608295821.

The spelling of 21860 in words is "twenty-one thousand, eight hundred sixty".