21993663 has 16 divisors (see below), whose sum is σ = 30468096. Its totient is φ = 14097120.

The previous prime is 21993649. The next prime is 21993667. The reversal of 21993663 is 36639912.

It is not a de Polignac number, because 21993663 - 2¹⁰ = 21992639 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21993667) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15406 + ... + 16772.

It is an arithmetic number, because the mean of its divisors is an integer number (1904256).

Almost surely, 2^21993663 is an apocalyptic number.

21993663 is a deficient number, since it is larger than the sum of its proper divisors (8474433).

21993663 is a wasteful number, since it uses less digits than its factorization.

21993663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1574.

The product of its digits is 52488, while the sum is 39.

The square root of 21993663 is about 4689.7401847011. The cubic root of 21993663 is about 280.1770266589.

The spelling of 21993663 in words is "twenty-one million, nine hundred ninety-three thousand, six hundred sixty-three".