21685317 has 16 divisors (see below), whose sum is σ = 29819520. Its totient is φ = 14011200.

The previous prime is 21685309. The next prime is 21685333. The reversal of 21685317 is 71358612.

21685317 is nontrivially palindromic in base 13.

It is not a de Polignac number, because 21685317 - 2³ = 21685309 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685817) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 12159 + ... + 13827.

It is an arithmetic number, because the mean of its divisors is an integer number (1863720).

Almost surely, 2^21685317 is an apocalyptic number.

It is an amenable number.

21685317 is a deficient number, since it is larger than the sum of its proper divisors (8134203).

21685317 is a wasteful number, since it uses less digits than its factorization.

21685317 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1804.

The product of its digits is 10080, while the sum is 33.

The square root of 21685317 is about 4656.7496174907. The cubic root of 21685317 is about 278.8615209293.

The spelling of 21685317 in words is "twenty-one million, six hundred eighty-five thousand, three hundred seventeen".