21809073 has 32 divisors (see below), whose sum is σ = 35360640. Its totient is φ = 11773440.

The previous prime is 21809071. The next prime is 21809087. The reversal of 21809073 is 37090812.

It is a happy number.

It is not a de Polignac number, because 21809073 - 2¹ = 21809071 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21809073.

It is not an unprimeable number, because it can be changed into a prime (21809071) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 11565 + ... + 13317.

It is an arithmetic number, because the mean of its divisors is an integer number (1105020).

Almost surely, 2^21809073 is an apocalyptic number.

It is an amenable number.

21809073 is a deficient number, since it is larger than the sum of its proper divisors (13551567).

21809073 is a wasteful number, since it uses less digits than its factorization.

21809073 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1809.

The product of its (nonzero) digits is 3024, while the sum is 30.

The square root of 21809073 is about 4670.0185224472. The cubic root of 21809073 is about 279.3909935341.

Adding to 21809073 its reverse (37090812), we get a palindrome (58899885).

The spelling of 21809073 in words is "twenty-one million, eight hundred nine thousand, seventy-three".