21684505 has 4 divisors (see below), whose sum is σ = 26021412. Its totient is φ = 17347600.

The previous prime is 21684499. The next prime is 21684511. The reversal of 21684505 is 50548612.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21684499) and next prime (21684511).

It can be written as a sum of positive squares in 2 ways, for example, as 12278016 + 9406489 = 3504^2 + 3067^2 .

It is not a de Polignac number, because 21684505 - 2¹³ = 21676313 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2168446 + ... + 2168455.

It is an arithmetic number, because the mean of its divisors is an integer number (6505353).

Almost surely, 2^21684505 is an apocalyptic number.

It is an amenable number.

21684505 is a deficient number, since it is larger than the sum of its proper divisors (4336907).

21684505 is an equidigital number, since it uses as much as digits as its factorization.

21684505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4336906.

The product of its (nonzero) digits is 9600, while the sum is 31.

The square root of 21684505 is about 4656.6624313987. The cubic root of 21684505 is about 278.8580402580.

The spelling of 21684505 in words is "twenty-one million, six hundred eighty-four thousand, five hundred five".