21216663 has 24 divisors (see below), whose sum is σ = 34948368. Its totient is φ = 12287232.

The previous prime is 21216659. The next prime is 21216707. The reversal of 21216663 is 36661212.

It is not a de Polignac number, because 21216663 - 2² = 21216659 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216263) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3345 + ... + 7322.

It is an arithmetic number, because the mean of its divisors is an integer number (1456182).

Almost surely, 2^21216663 is an apocalyptic number.

21216663 is a deficient number, since it is larger than the sum of its proper divisors (13731705).

21216663 is a wasteful number, since it uses less digits than its factorization.

21216663 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10703 (or 10700 counting only the distinct ones).

The product of its digits is 2592, while the sum is 27.

The square root of 21216663 is about 4606.1549040387. The cubic root of 21216663 is about 276.8379934302.

Adding to 21216663 its reverse (36661212), we get a palindrome (57877875).

The spelling of 21216663 in words is "twenty-one million, two hundred sixteen thousand, six hundred sixty-three".