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21845 = 517257
BaseRepresentation
bin101010101010101
31002222002
411111111
51144340
6245045
7120455
oct52525
932862
1021845
111545a
1210785
139c35
147d65
156715
hex5555

21845 has 8 divisors (see below), whose sum is σ = 27864. Its totient is φ = 16384.

The previous prime is 21841. The next prime is 21851. The reversal of 21845 is 54812.

21845 is nontrivially palindromic in base 2, base 4, base 8 and base 16.

21845 is an esthetic number in base 2, because in such base it adjacent digits differ by 1.

It can be written as a sum of positive squares in 4 ways, for example, as 11236 + 10609 = 106^2 + 103^2 .

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

It is a 7-Lehmer number, since φ(21845) divides (21845-1)7.

It is a cyclic number.

It is not a de Polignac number, because 21845 - 22 = 21841 is a prime.

It is the 16-th Jacobsthal number.

It is a Duffinian number.

21845 is an undulating number in base 2 and base 8.

It is a Curzon number.

21845 is a nontrivial repdigit in base 4 and base 16.

It is a plaindrome in base 4 and base 16.

It is a nialpdrome in base 4 and base 16.

It is a zygodrome in base 4 and base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21841) by changing a digit.

It is a nontrivial repunit in base 4.

In principle, a polygon with 21845 sides can be constructed with ruler and compass.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44 + ... + 213.

It is an arithmetic number, because the mean of its divisors is an integer number (3483).

21845 is a Friedman number, since it can be written as (4^8-1)/(5-2), using all its digits and the basic arithmetic operations.

221845 is an apocalyptic number.

It is an amenable number.

21845 is a deficient number, since it is larger than the sum of its proper divisors (6019).

21845 is a wasteful number, since it uses less digits than its factorization.

21845 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 279.

The product of its digits is 320, while the sum is 20.

The square root of 21845 is about 147.8005412710. The cubic root of 21845 is about 27.9544326865.

The spelling of 21845 in words is "twenty-one thousand, eight hundred forty-five".

Divisors: 1 5 17 85 257 1285 4369 21845