21809438 has 16 divisors (see below), whose sum is σ = 37947264. Its totient is φ = 9207000.

The previous prime is 21809429. The next prime is 21809443. The reversal of 21809438 is 83490812.

It is a happy number.

It is a Smith number, since the sum of its digits (35) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a junction number, because it is equal to n+sod(n) for n = 21809398 and 21809407.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10688 + ... + 12563.

It is an arithmetic number, because the mean of its divisors is an integer number (2371704).

Almost surely, 2^21809438 is an apocalyptic number.

21809438 is a deficient number, since it is larger than the sum of its proper divisors (16137826).

21809438 is a wasteful number, since it uses less digits than its factorization.

21809438 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23327.

The product of its (nonzero) digits is 13824, while the sum is 35.

The square root of 21809438 is about 4670.0576013578. The cubic root of 21809438 is about 279.3925521689.

The spelling of 21809438 in words is "twenty-one million, eight hundred nine thousand, four hundred thirty-eight".