21215 has 4 divisors (see below), whose sum is σ = 25464. Its totient is φ = 16968.

The previous prime is 21211. The next prime is 21221. The reversal of 21215 is 51212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21215 - 2² = 21211 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21196 and 21205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21211) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2117 + ... + 2126.

It is an arithmetic number, because the mean of its divisors is an integer number (6366).

2²¹²¹⁵ is an apocalyptic number.

21215 is a deficient number, since it is larger than the sum of its proper divisors (4249).

21215 is an equidigital number, since it uses as much as digits as its factorization.

21215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4248.

The product of its digits is 20, while the sum is 11.

The square root of 21215 is about 145.6536988888. The cubic root of 21215 is about 27.6830760222.

Adding to 21215 its reverse (51212), we get a palindrome (72427).

The spelling of 21215 in words is "twenty-one thousand, two hundred fifteen".