21680405 has 8 divisors (see below), whose sum is σ = 26116992. Its totient is φ = 17277328.

The previous prime is 21680381. The next prime is 21680413. The reversal of 21680405 is 50408612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21680405 - 2⁶ = 21680341 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6929 + ... + 9558.

It is an arithmetic number, because the mean of its divisors is an integer number (3264624).

Almost surely, 2^21680405 is an apocalyptic number.

It is an amenable number.

21680405 is a deficient number, since it is larger than the sum of its proper divisors (4436587).

21680405 is a wasteful number, since it uses less digits than its factorization.

21680405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16755.

The product of its (nonzero) digits is 1920, while the sum is 26.

The square root of 21680405 is about 4656.2221811250. Note that the first 3 decimals coincide. The cubic root of 21680405 is about 278.8404641127.

The spelling of 21680405 in words is "twenty-one million, six hundred eighty thousand, four hundred five".