21655 has 8 divisors (see below), whose sum is σ = 26784. Its totient is φ = 16800.

The previous prime is 21649. The next prime is 21661. The reversal of 21655 is 55612.

21655 = T₂₂ + T₂₃ + ... + T₅₁.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21649) and next prime (21661).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21655 - 2³ = 21647 is a prime.

It is a Duffinian number.

21655 is a lucky number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 270 + ... + 340.

It is an arithmetic number, because the mean of its divisors is an integer number (3348).

2²¹⁶⁵⁵ is an apocalyptic number.

21655 is a deficient number, since it is larger than the sum of its proper divisors (5129).

21655 is an equidigital number, since it uses as much as digits as its factorization.

21655 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137.

The product of its digits is 300, while the sum is 19.

The square root of 21655 is about 147.1563794064. The cubic root of 21655 is about 27.8731506880.

It can be divided in two parts, 21 and 655, that added together give a palindrome (676).

The spelling of 21655 in words is "twenty-one thousand, six hundred fifty-five".