21305215 has 8 divisors (see below), whose sum is σ = 26391168. Its totient is φ = 16494240.

The previous prime is 21305209. The next prime is 21305231. The reversal of 21305215 is 51250312.

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

It is not a de Polignac number, because 21305215 - 2¹⁷ = 21174143 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21305192 and 21305201.

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, 68572 + ... + 68881.

It is an arithmetic number, because the mean of its divisors is an integer number (3298896).

Almost surely, 2^21305215 is an apocalyptic number.

21305215 is a deficient number, since it is larger than the sum of its proper divisors (5085953).

21305215 is a wasteful number, since it uses less digits than its factorization.

21305215 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137489.

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

The square root of 21305215 is about 4615.7572509828. The cubic root of 21305215 is about 277.2226051444. Note that the first 3 decimals are identical.

Adding to 21305215 its reverse (51250312), we get a palindrome (72555527).

The spelling of 21305215 in words is "twenty-one million, three hundred five thousand, two hundred fifteen".