21687317 has 8 divisors (see below), whose sum is σ = 22064640. Its totient is φ = 21312720.

The previous prime is 21687307. The next prime is 21687329. The reversal of 21687317 is 71378612.

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 21687317 - 2⁴ = 21687301 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 (21687307) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 20903 + ... + 21915.

It is an arithmetic number, because the mean of its divisors is an integer number (2758080).

Almost surely, 2^21687317 is an apocalyptic number.

It is an amenable number.

21687317 is a deficient number, since it is larger than the sum of its proper divisors (377323).

21687317 is a wasteful number, since it uses less digits than its factorization.

21687317 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1363.

The product of its digits is 14112, while the sum is 35.

The square root of 21687317 is about 4656.9643545984. The cubic root of 21687317 is about 278.8700936407.

The spelling of 21687317 in words is "twenty-one million, six hundred eighty-seven thousand, three hundred seventeen".