21681679 has 16 divisors (see below), whose sum is σ = 23823360. Its totient is φ = 19656000.

The previous prime is 21681659. The next prime is 21681683. The reversal of 21681679 is 97618612.

It is a cyclic number.

It is not a de Polignac number, because 21681679 - 2⁷ = 21681551 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 (21681619) 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 15 ways as a sum of consecutive naturals, for example, 77019 + ... + 77299.

It is an arithmetic number, because the mean of its divisors is an integer number (1488960).

Almost surely, 2^21681679 is an apocalyptic number.

21681679 is a deficient number, since it is larger than the sum of its proper divisors (2141681).

21681679 is a wasteful number, since it uses less digits than its factorization.

21681679 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 462.

The product of its digits is 36288, while the sum is 40.

The square root of 21681679 is about 4656.3589853017. The cubic root of 21681679 is about 278.8459258156.

The spelling of 21681679 in words is "twenty-one million, six hundred eighty-one thousand, six hundred seventy-nine".