21217216 has 14 divisors (see below), whose sum is σ = 42103040. Its totient is φ = 10608576.

The previous prime is 21217199. The next prime is 21217223. The reversal of 21217216 is 61271212.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 165696 + ... + 165823.

It is an arithmetic number, because the mean of its divisors is an integer number (3007360).

Almost surely, 2^21217216 is an apocalyptic number.

It is an amenable number.

21217216 is a deficient number, since it is larger than the sum of its proper divisors (20885824).

21217216 is an equidigital number, since it uses as much as digits as its factorization.

21217216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 331531 (or 331521 counting only the distinct ones).

The product of its digits is 336, while the sum is 22.

The square root of 21217216 is about 4606.2149320239. The cubic root of 21217216 is about 276.8403986165.

Adding to 21217216 its reverse (61271212), we get a palindrome (82488428).

The spelling of 21217216 in words is "twenty-one million, two hundred seventeen thousand, two hundred sixteen".