21089917 has 4 divisors (see below), whose sum is σ = 21243996. Its totient is φ = 20935840.

The previous prime is 21089903. The next prime is 21089921. The reversal of 21089917 is 71998012.

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 9400356 + 11689561 = 3066^2 + 3419^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21089917 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 (21089947) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 76834 + ... + 77107.

It is an arithmetic number, because the mean of its divisors is an integer number (5310999).

Almost surely, 2^21089917 is an apocalyptic number.

It is an amenable number.

21089917 is a deficient number, since it is larger than the sum of its proper divisors (154079).

21089917 is a wasteful number, since it uses less digits than its factorization.

21089917 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 154078.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21089917 is about 4592.3759645743. The cubic root of 21089917 is about 276.2856255114.

The spelling of 21089917 in words is "twenty-one million, eighty-nine thousand, nine hundred seventeen".