21668687 has 4 divisors (see below), whose sum is σ = 21766080. Its totient is φ = 21571296.

The previous prime is 21668681. The next prime is 21668711. The reversal of 21668687 is 78686612.

21668687 = 194² + 195² + ... + 416².

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21668687 - 2¹⁸ = 21406543 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21668681) 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 in 3 ways as a sum of consecutive naturals, for example, 48362 + ... + 48807.

It is an arithmetic number, because the mean of its divisors is an integer number (5441520).

Almost surely, 2^21668687 is an apocalyptic number.

21668687 is a deficient number, since it is larger than the sum of its proper divisors (97393).

21668687 is an equidigital number, since it uses as much as digits as its factorization.

21668687 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 97392.

The product of its digits is 193536, while the sum is 44.

The square root of 21668687 is about 4654.9636948101. The cubic root of 21668687 is about 278.7902184122.

The spelling of 21668687 in words is "twenty-one million, six hundred sixty-eight thousand, six hundred eighty-seven".