21809709 has 32 divisors (see below), whose sum is σ = 33914880. Its totient is φ = 13834800.

The previous prime is 21809693. The next prime is 21809719. The reversal of 21809709 is 90790812.

It is a happy number.

It is not a de Polignac number, because 21809709 - 2⁴ = 21809693 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21809719) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 59244 + ... + 59610.

It is an arithmetic number, because the mean of its divisors is an integer number (1059840).

Almost surely, 2^21809709 is an apocalyptic number.

It is an amenable number.

21809709 is a deficient number, since it is larger than the sum of its proper divisors (12105171).

21809709 is a wasteful number, since it uses less digits than its factorization.

21809709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 478 (or 472 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 36.

The square root of 21809709 is about 4670.0866158991. The cubic root of 21809709 is about 279.3937093907.

The spelling of 21809709 in words is "twenty-one million, eight hundred nine thousand, seven hundred nine".