21406689 has 24 divisors (see below), whose sum is σ = 32963112. Its totient is φ = 13340160.

The previous prime is 21406663. The next prime is 21406699. The reversal of 21406689 is 98660412.

It can be written as a sum of positive squares in 4 ways, for example, as 90000 + 21316689 = 300^2 + 4617^2 .

It is not a de Polignac number, because 21406689 - 2¹² = 21402593 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21406699) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 27307 + ... + 28079.

It is an arithmetic number, because the mean of its divisors is an integer number (1373463).

Almost surely, 2^21406689 is an apocalyptic number.

It is an amenable number.

21406689 is a deficient number, since it is larger than the sum of its proper divisors (11556423).

21406689 is a wasteful number, since it uses less digits than its factorization.

21406689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 977 (or 974 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 21406689 is about 4626.7363227225. The cubic root of 21406689 is about 277.6620334436.

The spelling of 21406689 in words is "twenty-one million, four hundred six thousand, six hundred eighty-nine".