21061809 has 16 divisors (see below), whose sum is σ = 31359040. Its totient is φ = 13970880.

The previous prime is 21061783. The next prime is 21061819. The reversal of 21061809 is 90816012.

It is not a de Polignac number, because 21061809 - 2¹¹ = 21059761 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21061819) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3849 + ... + 7545.

It is an arithmetic number, because the mean of its divisors is an integer number (1959940).

Almost surely, 2^21061809 is an apocalyptic number.

It is an amenable number.

21061809 is a deficient number, since it is larger than the sum of its proper divisors (10297231).

21061809 is a wasteful number, since it uses less digits than its factorization.

21061809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3917 (or 3911 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 27.

The square root of 21061809 is about 4589.3146547170. The cubic root of 21061809 is about 276.1628292490.

The spelling of 21061809 in words is "twenty-one million, sixty-one thousand, eight hundred nine".