21688001 has 4 divisors (see below), whose sum is σ = 22043604. Its totient is φ = 21332400.

The previous prime is 21687997. The next prime is 21688013. The reversal of 21688001 is 10088612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2808976 + 18879025 = 1676^2 + 4345^2 .

It is a cyclic number.

It is not a de Polignac number, because 21688001 - 2² = 21687997 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21688301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 177710 + ... + 177831.

It is an arithmetic number, because the mean of its divisors is an integer number (5510901).

Almost surely, 2^21688001 is an apocalyptic number.

It is an amenable number.

21688001 is a deficient number, since it is larger than the sum of its proper divisors (355603).

21688001 is an equidigital number, since it uses as much as digits as its factorization.

21688001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 355602.

The product of its (nonzero) digits is 768, while the sum is 26.

The square root of 21688001 is about 4657.0377924170. The cubic root of 21688001 is about 278.8730253871.

The spelling of 21688001 in words is "twenty-one million, six hundred eighty-eight thousand, one".