21288689 has 4 divisors (see below), whose sum is σ = 21342180. Its totient is φ = 21235200.

The previous prime is 21288671. The next prime is 21288691. The reversal of 21288689 is 98688212.

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 12390400 + 8898289 = 3520^2 + 2983^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21288689 is a prime.

It is a super-3 number, since 3×21288689³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21288989) 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, 26144 + ... + 26945.

It is an arithmetic number, because the mean of its divisors is an integer number (5335545).

Almost surely, 2^21288689 is an apocalyptic number.

It is an amenable number.

21288689 is a deficient number, since it is larger than the sum of its proper divisors (53491).

21288689 is an equidigital number, since it uses as much as digits as its factorization.

21288689 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53490.

The product of its digits is 110592, while the sum is 44.

The square root of 21288689 is about 4613.9667315662. The cubic root of 21288689 is about 277.1509080530.

The spelling of 21288689 in words is "twenty-one million, two hundred eighty-eight thousand, six hundred eighty-nine".