21806129309 has 4 divisors (see below), whose sum is σ = 21826081116. Its totient is φ = 21786177504.

The previous prime is 21806129243. The next prime is 21806129311. The reversal of 21806129309 is 90392160812.

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 10098240100 + 11707889209 = 100490^2 + 108203^2 .

It is a cyclic number.

It is not a de Polignac number, because 21806129309 - 2⁸ = 21806129053 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21806129809) 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, 9974264 + ... + 9976449.

It is an arithmetic number, because the mean of its divisors is an integer number (5456520279).

Almost surely, 2^21806129309 is an apocalyptic number.

It is an amenable number.

21806129309 is a deficient number, since it is larger than the sum of its proper divisors (19951807).

21806129309 is a wasteful number, since it uses less digits than its factorization.

21806129309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19951806.

The product of its (nonzero) digits is 46656, while the sum is 41.

The spelling of 21806129309 in words is "twenty-one billion, eight hundred six million, one hundred twenty-nine thousand, three hundred nine".