21856843009 has 4 divisors (see below), whose sum is σ = 21983183316. Its totient is φ = 21730502704.

The previous prime is 21856842967. The next prime is 21856843013. The reversal of 21856843009 is 90034865812.

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 7868577025 + 13988265984 = 88705^2 + 118272^2 .

It is a cyclic number.

It is not a de Polignac number, because 21856843009 - 2⁷ = 21856842881 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21856843009.

It is not an unprimeable number, because it can be changed into a prime (21856843039) 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, 63169894 + ... + 63170239.

It is an arithmetic number, because the mean of its divisors is an integer number (5495795829).

Almost surely, 2^21856843009 is an apocalyptic number.

It is an amenable number.

21856843009 is a deficient number, since it is larger than the sum of its proper divisors (126340307).

21856843009 is a wasteful number, since it uses less digits than its factorization.

21856843009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 126340306.

The product of its (nonzero) digits is 414720, while the sum is 46.

The spelling of 21856843009 in words is "twenty-one billion, eight hundred fifty-six million, eight hundred forty-three thousand, nine".