21217215 has 8 divisors (see below), whose sum is σ = 33947568. Its totient is φ = 11315840.

The previous prime is 21217199. The next prime is 21217223. The reversal of 21217215 is 51271212.

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

It is not a de Polignac number, because 21217215 - 2⁴ = 21217199 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21217191 and 21217200.

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, 707226 + ... + 707255.

It is an arithmetic number, because the mean of its divisors is an integer number (4243446).

Almost surely, 2^21217215 is an apocalyptic number.

21217215 is a deficient number, since it is larger than the sum of its proper divisors (12730353).

21217215 is a wasteful number, since it uses less digits than its factorization.

21217215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1414489.

The product of its digits is 280, while the sum is 21.

The square root of 21217215 is about 4606.2148234749. The cubic root of 21217215 is about 276.8403942672.

Adding to 21217215 its reverse (51271212), we get a palindrome (72488427).

The spelling of 21217215 in words is "twenty-one million, two hundred seventeen thousand, two hundred fifteen".