21688405 has 8 divisors (see below), whose sum is σ = 27396000. Its totient is φ = 16437456.

The previous prime is 21688397. The next prime is 21688409. The reversal of 21688405 is 50488612.

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 21688405 - 2³ = 21688397 is a prime.

It is a super-2 number, since 2×21688405² = 940773822888050, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21688409) 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, 114055 + ... + 114244.

It is an arithmetic number, because the mean of its divisors is an integer number (3424500).

Almost surely, 2^21688405 is an apocalyptic number.

It is an amenable number.

21688405 is a deficient number, since it is larger than the sum of its proper divisors (5707595).

21688405 is a wasteful number, since it uses less digits than its factorization.

21688405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 228323.

The product of its (nonzero) digits is 15360, while the sum is 34.

The square root of 21688405 is about 4657.0811674267. The cubic root of 21688405 is about 278.8747569744.

The spelling of 21688405 in words is "twenty-one million, six hundred eighty-eight thousand, four hundred five".