21664667 has 2 divisors, whose sum is σ = 21664668. Its totient is φ = 21664666.

The previous prime is 21664663. The next prime is 21664703. The reversal of 21664667 is 76646612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21664667 - 2² = 21664663 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21664667.

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, 10832333 + 10832334.

It is an arithmetic number, because the mean of its divisors is an integer number (10832334).

Almost surely, 2^21664667 is an apocalyptic number.

21664667 is a deficient number, since it is larger than the sum of its proper divisors (1).

21664667 is an equidigital number, since it uses as much as digits as its factorization.

21664667 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 72576, while the sum is 38.

The square root of 21664667 is about 4654.5318776436. The cubic root of 21664667 is about 278.7729768508.

The spelling of 21664667 in words is "twenty-one million, six hundred sixty-four thousand, six hundred sixty-seven".