21664663 has 2 divisors, whose sum is σ = 21664664. Its totient is φ = 21664662.

The previous prime is 21664661. The next prime is 21664667. The reversal of 21664663 is 36646612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21664663 - 2¹ = 21664661 is a prime.

Together with 21664661, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21664661) by changing a digit.

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, 10832331 + 10832332.

It is an arithmetic number, because the mean of its divisors is an integer number (10832332).

Almost surely, 2^21664663 is an apocalyptic number.

21664663 is a deficient number, since it is larger than the sum of its proper divisors (1).

21664663 is an equidigital number, since it uses as much as digits as its factorization.

21664663 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 34.

The square root of 21664663 is about 4654.5314479548. The cubic root of 21664663 is about 278.7729596940.

The spelling of 21664663 in words is "twenty-one million, six hundred sixty-four thousand, six hundred sixty-three".