21499909 has 4 divisors (see below), whose sum is σ = 21577804. Its totient is φ = 21422016.

The previous prime is 21499901. The next prime is 21499913. The reversal of 21499909 is 90999412.

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 8381025 + 13118884 = 2895^2 + 3622^2 .

It is a cyclic number.

It is not a de Polignac number, because 21499909 - 2³ = 21499901 is a prime.

It is a Duffinian number.

It is a zygodrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21499901) 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, 38532 + ... + 39085.

It is an arithmetic number, because the mean of its divisors is an integer number (5394451).

Almost surely, 2^21499909 is an apocalyptic number.

It is an amenable number.

21499909 is a deficient number, since it is larger than the sum of its proper divisors (77895).

21499909 is an equidigital number, since it uses as much as digits as its factorization.

21499909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77894.

The product of its (nonzero) digits is 52488, while the sum is 43.

The square root of 21499909 is about 4636.7994349551. The cubic root of 21499909 is about 278.0644960169.

The spelling of 21499909 in words is "twenty-one million, four hundred ninety-nine thousand, nine hundred nine".