21682809 has 20 divisors (see below), whose sum is σ = 33185460. Its totient is φ = 14100480.

The previous prime is 21682757. The next prime is 21682823. The reversal of 21682809 is 90828612.

It can be written as a sum of positive squares in 2 ways, for example, as 1432809 + 20250000 = 1197^2 + 4500^2 .

It is not a de Polignac number, because 21682809 - 2⁷ = 21682681 is a prime.

It is a super-2 number, since 2×21682809² = 940288412260962, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21682849) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 57 + ... + 6585.

It is an arithmetic number, because the mean of its divisors is an integer number (1659273).

Almost surely, 2^21682809 is an apocalyptic number.

It is an amenable number.

21682809 is a deficient number, since it is larger than the sum of its proper divisors (11502651).

21682809 is an equidigital number, since it uses as much as digits as its factorization.

21682809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6582 (or 6573 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 36.

The square root of 21682809 is about 4656.4803231625. The cubic root of 21682809 is about 278.8507700041.

The spelling of 21682809 in words is "twenty-one million, six hundred eighty-two thousand, eight hundred nine".