21700809 has 12 divisors (see below), whose sum is σ = 33756996. Its totient is φ = 13354272.

The previous prime is 21700771. The next prime is 21700829. The reversal of 21700809 is 90800712.

It can be written as a sum of positive squares in 2 ways, for example, as 5419584 + 16281225 = 2328^2 + 4035^2 .

It is not a de Polignac number, because 21700809 - 2⁹ = 21700297 is a prime.

It is a super-2 number, since 2×21700809² = 941850222508962, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21700829) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 92622 + ... + 92855.

It is an arithmetic number, because the mean of its divisors is an integer number (2813083).

Almost surely, 2^21700809 is an apocalyptic number.

It is an amenable number.

21700809 is a deficient number, since it is larger than the sum of its proper divisors (12056187).

21700809 is a wasteful number, since it uses less digits than its factorization.

21700809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 185496 (or 185493 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 27.

The square root of 21700809 is about 4658.4127125020. The cubic root of 21700809 is about 278.9279113864.

The spelling of 21700809 in words is "twenty-one million, seven hundred thousand, eight hundred nine".