21405317 has 8 divisors (see below), whose sum is σ = 21649440. Its totient is φ = 21162960.

The previous prime is 21405313. The next prime is 21405337. The reversal of 21405317 is 71350412.

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 21405317 - 2² = 21405313 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21405292 and 21405301.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405313) 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, 48098 + ... + 48540.

It is an arithmetic number, because the mean of its divisors is an integer number (2706180).

Almost surely, 2^21405317 is an apocalyptic number.

It is an amenable number.

21405317 is a deficient number, since it is larger than the sum of its proper divisors (244123).

21405317 is a wasteful number, since it uses less digits than its factorization.

21405317 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 883.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 21405317 is about 4626.5880516856. The cubic root of 21405317 is about 277.6561013344.

Adding to 21405317 its reverse (71350412), we get a palindrome (92755729).

The spelling of 21405317 in words is "twenty-one million, four hundred five thousand, three hundred seventeen".