21798709 has 4 divisors (see below), whose sum is σ = 23081004. Its totient is φ = 20516416.

The previous prime is 21798703. The next prime is 21798727. The reversal of 21798709 is 90789712.

It is a happy number.

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 12404484 + 9394225 = 3522^2 + 3065^2 .

It is not a de Polignac number, because 21798709 - 2⁹ = 21798197 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 (21798703) 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, 641122 + ... + 641155.

It is an arithmetic number, because the mean of its divisors is an integer number (5770251).

Almost surely, 2^21798709 is an apocalyptic number.

It is an amenable number.

21798709 is a deficient number, since it is larger than the sum of its proper divisors (1282295).

21798709 is a wasteful number, since it uses less digits than its factorization.

21798709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1282294.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 21798709 is about 4668.9087590143. The cubic root of 21798709 is about 279.3467295855.

The spelling of 21798709 in words is "twenty-one million, seven hundred ninety-eight thousand, seven hundred nine".