21115 has 8 divisors (see below), whose sum is σ = 26208. Its totient is φ = 16320.
The previous prime is 21107. The next prime is 21121. The reversal of 21115 is 51112.
It is a happy number.
21115 is a nontrivial binomial coefficient, being equal to C(206, 2).
It is a sphenic number, since it is the product of 3 distinct primes.
It is not a de Polignac number, because 21115 - 23 = 21107 is a prime.
It is a Duffinian number.
21115 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, 154 + ... + 256.
It is an arithmetic number, because the mean of its divisors is an integer number (3276).
221115 is an apocalyptic number.
21115 is the 205-th triangular number and also the 103-rd hexagonal number.
21115 is the 69-th centered nonagonal number.
21115 is a deficient number, since it is larger than the sum of its proper divisors (5093).
21115 is a wasteful number, since it uses less digits than its factorization.
21115 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 149.
The product of its digits is 10, while the sum is 10.
The square root of 21115 is about 145.3100134196. The cubic root of 21115 is about 27.6395114274.
Adding to 21115 its reverse (51112), we get a palindrome (72227).
It can be divided in two parts, 2111 and 5, that added together give a square (2116 = 462).
The spelling of 21115 in words is "twenty-one thousand, one hundred fifteen".
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