21305806073 has 4 divisors (see below), whose sum is σ = 21707802468. Its totient is φ = 20903809680.

The previous prime is 21305806057. The next prime is 21305806091. The reversal of 21305806073 is 37060850312.

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

It can be written as a sum of positive squares in 2 ways, for example, as 7463577664 + 13842228409 = 86392^2 + 117653^2 .

It is a cyclic number.

It is not a de Polignac number, because 21305806073 - 2⁴ = 21305806057 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21305806273) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 200998118 + ... + 200998223.

It is an arithmetic number, because the mean of its divisors is an integer number (5426950617).

Almost surely, 2^21305806073 is an apocalyptic number.

It is an amenable number.

21305806073 is a deficient number, since it is larger than the sum of its proper divisors (401996395).

21305806073 is an equidigital number, since it uses as much as digits as its factorization.

21305806073 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 401996394.

The product of its (nonzero) digits is 30240, while the sum is 35.

The spelling of 21305806073 in words is "twenty-one billion, three hundred five million, eight hundred six thousand, seventy-three".