21681868 has 24 divisors (see below), whose sum is σ = 43267392. Its totient is φ = 9417984.

The previous prime is 21681839. The next prime is 21681871. The reversal of 21681868 is 86818612.

It is a plaindrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 21681868.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 11380 + ... + 13147.

It is an arithmetic number, because the mean of its divisors is an integer number (1802808).

Almost surely, 2^21681868 is an apocalyptic number.

It is an amenable number.

21681868 is a deficient number, since it is larger than the sum of its proper divisors (21585524).

21681868 is a wasteful number, since it uses less digits than its factorization.

21681868 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24561 (or 24559 counting only the distinct ones).

The product of its digits is 36864, while the sum is 40.

The square root of 21681868 is about 4656.3792800845. The cubic root of 21681868 is about 278.8467360500.

The spelling of 21681868 in words is "twenty-one million, six hundred eighty-one thousand, eight hundred sixty-eight".